1941 Axis momentum accelerates in WW2

WEBVTT
Kind: captions
Language: en

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- [Voiceover] As we've already
seen in the last few videos,

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with the war officially
starting in September of 1939,

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the Axis powers get momentum
through the end of 1939,

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all the way into 1940.

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That was the last video that
we covered and that takes us

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to 1941 and what we're
gonna see in 1941 which is

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the focus of this video is
that the Axis powers only seem

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to gain more momentum.

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Because of all of that momentum they

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perhaps gets a little bit
overconfident and stretch

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themselves or begin to
stretch themselves too thin.

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So let's think about what happens in 1941.

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So, if we talk about early
1941 or the Spring of 1941,

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in March, Bulgaria decides
to join the Axis powers.

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You can imagine there's a lot
of pressuring applied to them

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and they kind of see
where the momentum is.

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Let's be on that side.

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Bulgaria joins the Axis and then in

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North Africa you might remember
that in 1940, the Allies,

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in particular, the British,
were able to defeat the Italians

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and push them back into Libya
but now in March of 1941, the

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Italians get reinforcements,
Italian reinforcements and also

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German reinforcements
under the command of Rommel

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the Desert Fox, famous desert
commander and they are able to

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push the British back to the
Egyptian border and they also

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take siege of the town of Tobruk.

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Now, you might have

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noticed something that I just drew.

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The supply lines in the

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North Africa campaign are very,
very, very long and that's

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part of the reason why there's one side.

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One side has supply lines and as they

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start to make progress and as the Allies

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make progress and push into
Libya, their supply lines got

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really long and so the other

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side has an easier timely supply.

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Then as the Axis pushes
the Allies back into Egypt,

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then their supply lines get
really long and the other

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side...it makes it easier for
them to resupply and so North

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Africa is kind of defined by
this constant back and forth.

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But, by early 1941, it looks
like the Axis is on the

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offensive, able to push the
British back into Egypt lay

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siege to the town of Tobruk.

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So, let me write this
down as North Africa.

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So, I'll just say North
Africa over here or

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I'll could say Rommel in North Africa

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pushing the British back.

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And then we can start
talking about what happens in

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the Balkans and this is still
in Spring as we go into April

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of 1941 and just as a little
bit of background here, and

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frankly I should have covered
it a couple of videos ago.

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As far back as 1939, actually
before World War II officially

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started, in Spring of 1939,
Italy actually occupies Albania

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so this actually should
have already been red.

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This is in 1939 that this happens and

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then at the end of 1940, Italy

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uses Albania as a base of
operation to try to invade Greece

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but they are pushed back.

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Actually one of the reasons why

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the British we able to be
pushed back in North Africa is

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after they were successful
against the Italians, most of the

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bulk of the British forces we
sent to Greece to help defend

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Greece at the end of 1940.

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So, in 1939, Albania gets taken

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over by Italy and at the end
of 1940...October 1940, Greece

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is invaded by Italy but they
are then pushed back but to

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help the Greeks, the Allies
send many of the forces that

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were in North Africa after they
were successful against the

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Italians in Libya.

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Now, as we go into April of 1941... that

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was all background, remember
Albania before the war started

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in April 1939, October 1940
was Italy's kind of first push

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into Greece and it was unsuccessful.

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Then the Greeks get
support from the Allies

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in North Africa and now as we go

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into 1941, the Germans start
supporting and really take

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charge in Balkans and in Greece
and so with the help of the

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Germans the Axis is able to
take over Yugoslavia and Greece

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and start aerial bombardment of Crete.

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So, once again, we're not
even halfway through the year

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in 1941 and we see a huge

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swath of Europe is under the
control of the Axis powers.

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And now we go into the summer of 1941.

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This is actually a pivotal
move, what's about to happen.

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Now you can imagine that the Axis powers,

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in particular, Hitler, are feeling

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pretty confident.

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We are only about that far into the war.

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So we're not even two years
into the war yet and it looks

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like the Axis is going to win.

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Now you might remember that

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they have a pact with the Soviet Union.

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Hey, we're gonna split
a lot of Eastern Europe

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into our spheres of influence

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so to speak, but now Hitler's
like, well, I think I'm ready

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to attack and when you attack

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the Soviet Union really matters.

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You do not want to attack
the Soviet Union in the

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winter...or Russia in the winter.

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Russia's obviously at the

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heart of the Soviet Union.

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That something that Napoleon learned.

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Many military commanders have learnt.

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You do not want to be fighting in Russia

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over the winter, so summer of

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1941, Hitler figures, hey,
this is the Axis chance.

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And so, in June, he decides
to attack the Soviet Union.

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So, this is a very, very, very
bold move because now they're

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fighting the British.

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Remember, the British are kind of not

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a joke to be battling out
here in Western Europe and now

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they're going to be taking on
the Soviet Union in the east,

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a major, major world power.

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But at first, like always, it

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seems like it's going
well for the Germans.

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By September, they're able to

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push up all the way to Leningrad.

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So, this is September of 1941
and lay lay siege and begin

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laying siege to that town.

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This is kind of a long bloody
siege that happens there.

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So, we're right now, right about there.

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And most historians would tell
you that this was one of the

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mistakes of Adolph Hitler
because now he is stretched very,

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very, very thin.

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He has to fight two world powers, Soviet

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Union and Great Britain and the
United States hasn't entered

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into the war yet and that's
what we're about to get into

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because if we go into Asia it

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was still in 1941 what happens in July.

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So, little bit after
Hitler decides to start

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invading the Soviet Union going
back on the pact, the non-

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aggression pact.

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In July, you could imagine the US, they

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were never pleased with what's
been happening, what the

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Empire of Japan has been doing
in the Pacific, what they've

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been doing in China, in
Manchuria or even in terms of the

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war in China, the second
Sino Japanese War.

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They weren't happy of the Japanese

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taking over French Indochina.

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There's a big world power
here, the Empire of Japan.

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There's a big world power here,
the United States, that has

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a lot of possessions in the
Pacific and so, the United

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States in July of 1941...So
remember, this is still all

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1941, this is the same
year...decides to freeze the assets

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of Japan and probably the most
important part of that was an

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oil embargo of Japan.

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This is a big, big deal.

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Japan is fighting a major

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conflict with the Chinese.

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It's kind of flexing it's imperial muscles

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but it does not have many

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natural resources in and of
itself and in fact, that's one

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of the reasons why it's trying
to colonize other places to

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get more control of natural resources.

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And now if it's fighting a war it doesn't

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have it's own oil resources and

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now there's an oil embargo of
Japan and the United States at

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the time was major oil producer
and even today, it's major

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oil producer.

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This was a big deal to
the Japanese because

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some estimates say they only
had about two years of reserves

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and they were fighting a war
where they might have to touch

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their reserves even more.

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So, you could imagine the

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Japanese, they want to have
their imperial ambitions.

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They probably want, especially now

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with this oil embargo, they

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probably want to take over
more natural resources and they

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probably want to knock out the
US or at least keep the US on

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its heels so the US can't
stop Japan from doing what it

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wants to do.

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So, all it wants in
December 1941, that's over

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the course of December 7th
and 8th, and it gets a little

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confusing because a lot
of this happens across the

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International Date Line.

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But over the course of December 7th

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and 8th, Japan goes on the
offensive in a major way in the

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Pacific.

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Over the course of several
hours, at most, a day,

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Japan is able to attack
Malaya, which is a British

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possession.

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It's able to attack Pearl
Harbor, where the US

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Pacific fleet is in hope to
knock out the US Pacific fleet

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so the US will have trouble
stopping Japan from doing

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whatever Japan wants to do.

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In the US, we focus a lot on

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Pearl Harbor but this was just
one of the attacks in this

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whole kind of several hours
of attacks where Japan went on

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the offensive.

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So, we have Malaya, we
have Pearl Harbor, we

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have Singapore, we have Guam,
we have (which was the US

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military base), Wake Island.

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You have the Philippines, which

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was a US possession ever since
the Spanish American war.

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You have Hong Kong, which is
a British possession and then

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shortly after that as you get
further into December, so this

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is kind of when you have Japan offensive.

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Then as you go on into later Decemeber,

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the kind of real prize for Japan was

00:11:05.218 --> 00:11:08.934
what we would now call Indonesia
but the Dutch East Indies.

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On this map it says
Netherlands East Indies.

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You have to remember the
Netherlands had been overrun.

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They're the low countries they were

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already overrun by German forces so the

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Japanese say hey, look there
are a lot of resources here,

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natural resources, especially oil.

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Let's go for this and so

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by the end of 1941, they're
also going for the Dutch East

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Indies and for Burma so you
could imagine it's a very

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aggressive, very, very bold
move on Japan but they kind of

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had imperial ambitions.

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They were afraid of they access to

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natural resources so they went
for it but obviously one of

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the major consequence of this
is the United States was not

00:11:50.126 --> 00:11:52.262
happy about this and they

00:11:52.262 --> 00:11:54.538
were already sympathetic to the Allies.

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They didn't like what was
going on in Europe either.

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They didn't like what was
going on in China and so that

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causes the United States to
enter into World War II on the

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side of the Allies and then
the Axis powers to declare war

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on the United States,
which was a big deal.


1940 - Axis gains momentum in World War II

WEBVTT
Kind: captions
Language: en

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Where we left off in the last video,
World War II had begun.

00:00:03.424 --> 00:00:08.148
In September of 1939
Germany invades Poland.

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Followed shortly by France and
Great Britain declaring war on Germany

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Followed shortly by the Soviet Union
themselves under Stalin's leadership,

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also invading Poland and laying claim
to their sphere of influence.

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And so now we are going to enter into 1940.
And were going to see that in 1940 and 1941

00:00:25.945 --> 00:00:32.490
things only start to accelerate in the Nazis',
and, as we'll soon call them, the Axis Powers' favor.

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So in April,

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you have the Germans
invade Denmark and Norway

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...Denmark and Norway...

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...let me make sure that I spell that right...

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So Germany invades Denmark and Norway.

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This is April of 1940.

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and then you have May of 1940
Germany invades the Netherlands and Belgum.

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So Netherlands....
let me just write...let me write...

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The Low Countries it's sometimes called
because this place,

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the land in the Netherlands, right over here, is very close to sea level or sometimes even below sea level.

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Low Countries

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So invades Netherlands, invades Belgium.

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Kind of, kind of very similar
to what happened in World War I,

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where that's kind of how Germany gets to France.

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And then in June, in June, Italy enters the fray.

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Italy, which we've seen before, Italy declares war.

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Italy in the war, Benito Mousselini in the run-up to World War II is getting closer and closer to Adolf Hitler.

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And so, in June, Italy declares war on the Allies, on Great Britain and France.

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And so now Italy, so now Italy is formally in World War II.

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And as soon as Italy joins World War II, you start having all these skirmishes out here between Italy's colonies,

00:02:00.442 --> 00:02:03.207
and it's kind of where they're ruling colonially,

00:02:03.207 --> 00:02:09.297
in Libya, and in Egypt where the
British are essentially in control.

00:02:09.297 --> 00:02:14.482
So you start having all of these skirmishes across the border, the Egyptian and Libyan border.

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So that was, that was June,
and actually June, Italy is into the war.

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And then shortly thereafter
France falls to Germany.

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So this wasn't like World War I where we get kind of embroiled in all this trench warfare,

00:02:27.804 --> 00:02:30.353
that lasts over the duration of most of the war;

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very quickly, think about it, this is only what...
eight, nine months into the war.

00:02:35.924 --> 00:02:40.312
France falls, a major power, France falls to Germany.

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And they install Vichy France, which at
first is in control for the part of France

00:02:46.052 --> 00:02:47.864
roughly the part of France that I'm highlighting.

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This the town of Vichy, which was the capitol of Vichy France.

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Which is why it's called that.

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And then later the rest of what's called Free France
falls to Germany, later in the war in 1942.

00:02:57.548 --> 00:03:05.595
But things are really, really not looking good for the Allies.

00:03:05.595 --> 00:03:11.208
So France falls, falls to Germany,

00:03:11.208 --> 00:03:15.938
the establishment of Vichy France, which is
essentially controlled by the Germans,

00:03:15.938 --> 00:03:21.287
and then in July, Germany begins bombing Britain.

00:03:22.087 --> 00:03:26.087
So bombing... bombing Britain.

00:03:26.379 --> 00:03:29.985
The famous Battle of Britain, which was actually called
The Battle of Britain even before it began.

00:03:29.985 --> 00:03:34.065
Winston Churchill said, hey, we have to prepare for the upcoming Battle of Britain.

00:03:34.608 --> 00:03:38.098
And Germany starts bombing Great Britain.

00:03:39.014 --> 00:03:42.914
And then thing get only worse from there.

00:03:43.346 --> 00:03:50.482
So in September, in September the Axis forms
with Japan, Japan joining.

00:03:50.482 --> 00:03:55.297
Japan signs the Tripartite Pact, and so becomes...

00:03:55.297 --> 00:03:58.872
...the Axis forms between Japan Italy and Germany.

00:03:58.872 --> 00:04:08.342
...signs Tripartite Pact....

00:04:08.925 --> 00:04:15.715
So Japan is in the mix, and since France is already fallen to Germany.

00:04:16.136 --> 00:04:20.276
So Japan is now formally part of the Axis with Italy and Germany

00:04:20.281 --> 00:04:22.748
And since France has fallen to Germany,

00:04:22.875 --> 00:04:27.482
Japan says, hey, maybe we can go after some of France's colonies, and in particular French-Indochina,

00:04:27.651 --> 00:04:30.004
which we now refer to as Vietnam and Cambodia.

00:04:30.004 --> 00:04:36.612
And so, shortly thereafter, Japan attacks French Indo-China.

00:04:36.612 --> 00:04:38.942
so things are not really looking good at all.

00:04:38.942 --> 00:04:42.252
and it only gets worse from there.

00:04:42.492 --> 00:04:47.365
In November... so once again we're
a little over a year into the war now,

00:04:47.365 --> 00:04:52.356
we're entering the end of 1940, in November,

00:04:52.356 --> 00:04:55.336
Hungary and Romania are pressured to join the Axis

00:04:56.354 --> 00:05:02.168
So Hungary and Romania join the Axis

00:05:02.168 --> 00:05:10.163
So as we see as we kind of are leaving 1940, things
are not looking good at all for the Allied powers.

00:05:10.163 --> 00:05:12.654
You see this map, and I apologize for my messiness,

00:05:12.654 --> 00:05:15.451
it's looking more and more and more red.

00:05:15.451 --> 00:05:24.177
The only slightly, kind of, saving grace for the Allied Powers is what's happening over here in North Africa,

00:05:24.177 --> 00:05:33.762
is that eventually the end of 1940, the British are able to drive the Italians back into Libya.

00:05:33.762 --> 00:05:36.969
So let me do this in a different color,
I'll do blue for the Allies

00:05:36.969 --> 00:05:43.645
So the British are able to drive
the Italian forces back into Libya.

00:05:43.645 --> 00:05:47.545
And they are essentially able to defeat the Italians in Libya,

00:05:47.545 --> 00:05:52.048
and, but that's only going to take us into 1941,
which I'll talk about in the next video,

00:05:52.048 --> 00:05:54.887
where the Germans send reinforcements under the command of Rommel,

00:05:54.887 --> 00:05:55.887
and they're able to drive the
British back again into Egypt,

00:05:55.887 --> 00:06:02.096
and we'll see in 1941 Germany
and the Axis Powers

00:06:02.096 --> 00:06:05.336
only become more and more
and more aggressive.

00:06:05.336 --> 00:06:12.464
And as we enter the end of 1941 we'll see
the entry of the US into World War II.


Beginning of World War II

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:05.028
World War II was the largest conflict
in all of human history.

00:00:05.031 --> 00:00:06.919
The largest and bloodiest conflict

00:00:06.919 --> 00:00:09.285
And so you can imagine it is quite complex

00:00:09.285 --> 00:00:15.659
My goal in this video is to start giving
us a survey, an overview of the war.

00:00:15.659 --> 00:00:18.103
And I won't even be able to cover it all in this video.

00:00:18.103 --> 00:00:21.243
It is really just a think about how did things get started.

00:00:21.243 --> 00:00:23.186
Or what happened in the lead up?

00:00:23.207 --> 00:00:27.667
And to start I am actually going to focus
on Asia and the Pacific.

00:00:27.851 --> 00:00:33.468
Which probably doesn't get enough attention
when we look at it from a western point of view

00:00:33.478 --> 00:00:36.088
But if we go back even to the early 1900s.

00:00:36.088 --> 00:00:39.033
Japan is becoming more and more militaristic.

00:00:39.068 --> 00:00:40.588
More and more nationalistic.

00:00:40.703 --> 00:00:43.417
In the early 1900s it had already occupied...

00:00:43.417 --> 00:00:47.927
It had already occupied Korea as of 1910.

00:00:47.927 --> 00:00:51.167
and in 1931 it invades Manchuria.

00:00:51.167 --> 00:00:53.457
It invades Manchuria.

00:00:53.457 --> 00:00:58.857
So this right over here, this is in 1931.

00:00:58.911 --> 00:01:03.801
And it installs a puppet state,
the puppet state of Manchukuo.

00:01:03.848 --> 00:01:06.359
And when we call something a puppet state,

00:01:06.359 --> 00:01:07.860
it means that there is a government there.

00:01:07.860 --> 00:01:11.437
And they kind of pretend to be in charge.

00:01:11.437 --> 00:01:15.257
But they're really controlled like
a puppet by someone else.

00:01:15.257 --> 00:01:18.548
And in this case it is the Empire of Japan.

00:01:18.548 --> 00:01:22.644
And we do remember what is happening in China in the 1930s.

00:01:22.644 --> 00:01:25.634
China is embroiled in a civil war.

00:01:25.634 --> 00:01:30.194
So there is a civil war going on in China.

00:01:30.305 --> 00:01:32.922
And that civil war is between

00:01:32.922 --> 00:01:37.242
the Nationalists, the Kuomintang
and the Communists

00:01:37.246 --> 00:01:41.198
versus the Communists

00:01:41.198 --> 00:01:43.879
The Communists led by Mao Zedong.

00:01:43.879 --> 00:01:47.401
The Kuomintang led by general Chiang Kai-shek.

00:01:47.401 --> 00:01:49.361
And so they're in the midst of the civil war.

00:01:49.363 --> 00:01:52.958
So you can imagine Imperial Japan
is taking advantage of this

00:01:52.958 --> 00:01:57.313
to take more and more control
over parts of China

00:01:57.313 --> 00:01:59.903
And that continues through the 30s

00:01:59.903 --> 00:02:02.026
until we get to 1937.

00:02:02.026 --> 00:02:06.146
And in 1937 the Japanese use some pretext

00:02:06.146 --> 00:02:09.194
with, you know, kind of a false flag, kind of...

00:02:09.194 --> 00:02:11.814
well, I won't go into the depths of what started it

00:02:11.814 --> 00:02:14.376
kind of this Marco-Polo Bridge Incident

00:02:14.376 --> 00:02:16.386
But it uses that as justifications

00:02:16.386 --> 00:02:19.978
to kind of have an all-out war with China

00:02:19.978 --> 00:02:25.690
so 1937...you have all-out war

00:02:25.690 --> 00:02:30.309
and this is often referred to as
the Second Sino-Japanese War

00:02:30.309 --> 00:02:34.900
...Sino-Japanese War

00:02:34.900 --> 00:02:38.070
Many historians actually would even consider
this the beginning of World War II.

00:02:38.070 --> 00:02:42.549
While, some of them say, ok this is the beginning of the Asian Theater of World War II

00:02:42.549 --> 00:02:45.398
of the all-out war between Japan and China,

00:02:45.398 --> 00:02:49.939
but it isn't until Germany invades Poland
in 1939 that you truly have

00:02:49.939 --> 00:02:53.379
the formal beginning, so to speak,
of World War II.

00:02:53.387 --> 00:02:56.504
Regardless of whether you consider this
the formal beginning or not,

00:02:56.504 --> 00:02:58.941
the Second Sino-Japanese War,
and it's called the second because

00:02:58.941 --> 00:03:01.522
there was another Sino-Japanese War
in the late 1800s

00:03:01.522 --> 00:03:03.968
that was called
the First Sino-Japanese War,

00:03:03.968 --> 00:03:08.790
this is incredibly, incredibly brutal
and incredibly bloody

00:03:08.790 --> 00:03:10.996
a lot of civilians affected

00:03:10.996 --> 00:03:14.562
we could do a whole series of videos
just on that

00:03:14.562 --> 00:03:16.491
But at this point it does become all-out war

00:03:16.491 --> 00:03:19.941
and this causes the civil war
to take a back seat

00:03:19.941 --> 00:03:24.617
to fighting off the aggressor
of Japan in 1937.

00:03:24.617 --> 00:03:29.519
So that lays a foundation for what's happening
in The Pacific, in the run-up to World War II.

00:03:29.519 --> 00:03:32.502
And now let's also remind ourselves
what's happening...

00:03:32.502 --> 00:03:34.353
what's happening in Europe.

00:03:34.353 --> 00:03:37.276
As we go through the 1930s

00:03:37.276 --> 00:03:40.816
Hitler's Germany, the Nazi Party,
is getting more and more militaristic.

00:03:40.816 --> 00:03:43.285
So this is Nazi Germany...

00:03:44.460 --> 00:03:47.080
Nazi Germany right over here.

00:03:47.080 --> 00:03:50.641
They're allied with Benito Mussolini's Italy.

00:03:50.641 --> 00:03:56.935
They're both extremely nationalistic;
they both do not like the Communists, at all

00:03:56.935 --> 00:04:00.853
You might remember, that in 1938...

00:04:00.853 --> 00:04:05.927
1938, you have the Anschluss,
which I'm sure I'm mispronouncing,

00:04:05.927 --> 00:04:10.537
and you also have the takeover
of the Sudetenland in Czechoslovakia.

00:04:10.537 --> 00:04:14.352
So the Anschluss was the unification with Austria

00:04:14.352 --> 00:04:18.563
and then you have the Germans taking over the of Sudetenland in Czechoslovakia

00:04:18.563 --> 00:04:20.508
and this is kind of the famous,
you know,

00:04:20.508 --> 00:04:23.977
the rest of the, what will be called the Allied Powers

00:04:23.977 --> 00:04:27.221
kind of say, "Okay, yeah, okay maybe Hitler's
just going to just do that...

00:04:27.221 --> 00:04:29.119
well we don't want to start another war.

00:04:29.119 --> 00:04:31.914
We still all remember World War I; it was really horrible.

00:04:31.914 --> 00:04:37.282
And so they kind of appease Hitler
and he's able to, kind of, satisfy his aggression.

00:04:37.282 --> 00:04:43.472
so in 1938 you have Austria,
Austria and the Sudetenland

00:04:43.472 --> 00:04:47.052
...and the Sudetenland...

00:04:47.052 --> 00:04:50.241
are taken over,
are taken over by Germany

00:04:50.241 --> 00:04:55.797
and then as you go into 1939,
as you go into 1939

00:04:55.797 --> 00:04:59.539
in March they're able to take over
all of Czechoslovakia

00:04:59.539 --> 00:05:02.036
they're able to take over
all of Czechoslovakia

00:05:02.036 --> 00:05:05.459
and once again the Allies are kind of,
they're feeling very uncomfortable,

00:05:05.459 --> 00:05:08.530
they kind of, have seen something like this before

00:05:08.530 --> 00:05:11.488
they would like to push back, but they still are,

00:05:11.488 --> 00:05:15.167
kind of, are not feeling good
about starting another World War

00:05:15.167 --> 00:05:18.347
so they're hoping that maybe Germany stops there.

00:05:18.347 --> 00:05:20.083
So let me write this down...

00:05:20.083 --> 00:05:23.081
So all of Czechoslovakia...

00:05:23.081 --> 00:05:27.952
...Czechoslovakia...
is taken over by the Germans.

00:05:27.952 --> 00:05:32.616
This is in March of 1939.

00:05:32.616 --> 00:05:38.079
And then in August you have the Germans,
and this is really in preparation for,

00:05:38.079 --> 00:05:41.284
what you could guess is about to happen,
for the all-out war that's about to happen

00:05:41.284 --> 00:05:43.865
the Germans don't want to fight
the Soviets right out the gate,

00:05:43.865 --> 00:05:49.364
as we will see, and as you might know,
they do eventually take on the Soviet Union,

00:05:49.364 --> 00:05:53.748
but in 1939 they get into a pact with
the Soviet Union.

00:05:53.748 --> 00:05:56.387
And so this is, they sign

00:05:56.387 --> 00:06:05.631
the Molotov–Ribbentrop Pact

00:06:05.631 --> 00:06:09.406
with the Soviet Union,
this is in August,

00:06:09.406 --> 00:06:11.933
which is essentially
mutual non-aggression

00:06:11.933 --> 00:06:14.404
"Hey, you know, you do what you need to do,
we know what we need to do."

00:06:14.404 --> 00:06:17.723
and they secretly started saying
"Okay were gonna, all the countries out here,

00:06:17.723 --> 00:06:19.601
we're going to create these
spheres of influence

00:06:19.601 --> 00:06:22.456
where Germany can take, uh,
control of part of it

00:06:22.456 --> 00:06:26.392
and the Soviet Union, and Stalin is in charge
of the Soviet Union at this point,

00:06:26.392 --> 00:06:28.409
can take over other parts of it.

00:06:28.409 --> 00:06:31.324
And then that leads us to the formal start

00:06:31.324 --> 00:06:34.346
where in September,
let me write this in a different color...

00:06:34.346 --> 00:06:40.436
so September of 1939,
on September 1st, Germany invades Poland

00:06:40.436 --> 00:06:44.402
Germany invades Poland on September 1st,

00:06:44.402 --> 00:06:48.973
which is generally considered
the beginning of World War II.

00:06:48.973 --> 00:06:55.874
and then you have the Great Britain and France declares war on Germany

00:06:55.874 --> 00:06:58.084
so let me write this

00:06:58.084 --> 00:07:04.831
World War II... starts

00:07:04.831 --> 00:07:08.502
everyone is declaring war on each other,
Germany invades Poland,

00:07:08.502 --> 00:07:12.072
Great Britain and France
declare war on Germany,

00:07:12.072 --> 00:07:13.363
and you have to remember at this point

00:07:13.363 --> 00:07:18.966
Stalin isn't so concerned about Hitler
he's just signed the Molotov-Ribbentrop Pact

00:07:18.966 --> 00:07:24.138
and so in mid-September, Stalin himself invades Poland as well

00:07:24.138 --> 00:07:27.544
so they both can kind of carve out...

00:07:27.544 --> 00:07:32.743
...their spheres of influence...

00:07:32.743 --> 00:07:38.383
so you can definitely sense that things are
not looking good for the world at this point

00:07:38.383 --> 00:07:42.131
you already have Asia in the
Second Sino-Japanese War,

00:07:42.131 --> 00:07:43.766
incredibly bloody war,

00:07:43.766 --> 00:07:45.541
and now you have kind of,

00:07:45.541 --> 00:07:48.510
a lot of very similar actors
that you had in World War I

00:07:48.510 --> 00:07:53.330
and then they're starting to get into
a fairly extensive engagement.


Adding mixed numbers introduction

WEBVTT
Kind: captions
Language: en

00:00:00.248 --> 00:00:01.641
- [Voiceover] Let's give
ourselves some practice

00:00:01.641 --> 00:00:03.766
adding mixed numbers.

00:00:03.766 --> 00:00:07.550
So let's say I want to add
two, let me write it this way.

00:00:07.550 --> 00:00:12.206
Let's say I want to add
two and four sevenths

00:00:12.206 --> 00:00:17.206
plus three and two sevenths,
three and two sevenths.

00:00:19.322 --> 00:00:20.959
I encourage you to pause this video

00:00:20.959 --> 00:00:24.297
and try to think about
what this is going to be.

00:00:24.383 --> 00:00:26.844
Well there's a couple of ways
that you could tackle it.

00:00:26.844 --> 00:00:28.791
One way, you could say, well let me just

00:00:28.791 --> 00:00:30.614
add the nonfraction parts.

00:00:30.614 --> 00:00:35.614
You could say that two plus
three is equal to five,

00:00:35.930 --> 00:00:40.930
and then you could say that
four sevenths plus two sevenths

00:00:41.491 --> 00:00:44.753
is equal to well four
sevenths plus two sevenths

00:00:44.753 --> 00:00:47.133
is gonna be equal to six sevenths.

00:00:47.133 --> 00:00:49.374
Hey, wait, wait, wait, how
did I, how did I do that?

00:00:49.374 --> 00:00:51.254
How did I just only add the fraction parts

00:00:51.254 --> 00:00:52.613
or add the whole parts?

00:00:52.613 --> 00:00:54.029
Well the way I did that is because

00:00:54.029 --> 00:00:55.968
two and four sevenths is the same thing

00:00:55.968 --> 00:00:59.694
as two plus four sevenths.

00:00:59.694 --> 00:01:03.188
Two and four sevenths, same
thing as two plus four sevenths.

00:01:03.188 --> 00:01:06.694
And then plus three and two
sevenths is the same thing

00:01:06.694 --> 00:01:09.910
as three plus two sevenths,

00:01:09.910 --> 00:01:12.232
so all I did over here,
two and four sevenths

00:01:12.232 --> 00:01:13.474
plus three and two sevenths,

00:01:13.474 --> 00:01:16.771
is two plus four sevenths
plus three plus two sevenths.

00:01:16.771 --> 00:01:20.730
And you can swap the
order in how this happens.

00:01:20.730 --> 00:01:23.713
So you could take, you
could just switch the order

00:01:23.713 --> 00:01:28.693
and say this is going to be
two plus three, two plus three,

00:01:28.693 --> 00:01:33.693
plus four sevenths, plus two sevenths.

00:01:37.644 --> 00:01:40.964
And what we just figured out was that

00:01:40.964 --> 00:01:44.586
two plus three is equal
to five, right over here,

00:01:44.586 --> 00:01:46.409
and that four sevenths plus two sevenths

00:01:46.409 --> 00:01:51.409
is equal to six sevenths, just like that.

00:01:52.863 --> 00:01:55.266
Now let's do a more interesting example.

00:01:55.266 --> 00:02:00.266
Let's do, let's say that I
have three and three fifths,

00:02:04.623 --> 00:02:09.623
three and three fifths
plus five and four fifths.

00:02:14.886 --> 00:02:17.683
Now what is this going to be equal to?

00:02:17.683 --> 00:02:19.668
Well if you do the same technique,

00:02:19.668 --> 00:02:24.126
if you add the three plus the five,

00:02:24.126 --> 00:02:26.007
you're going to get eight,

00:02:26.007 --> 00:02:31.007
and then if you add the three
fifths plus four fifths,

00:02:31.022 --> 00:02:33.147
you would get seven fifths.

00:02:33.147 --> 00:02:35.666
So you get eight and seven fifths.

00:02:35.666 --> 00:02:37.883
And this wouldn't be wrong.

00:02:37.883 --> 00:02:39.427
This is eight and seven fifths,

00:02:39.427 --> 00:02:40.983
if you add these two things together,

00:02:40.983 --> 00:02:42.805
but it's a little bit strange here

00:02:42.805 --> 00:02:45.580
because seven fifths
is bigger than a whole.

00:02:45.580 --> 00:02:47.797
So to get a better sense of what number's

00:02:47.797 --> 00:02:49.306
really being represented here,

00:02:49.306 --> 00:02:50.641
I want to rewrite this.

00:02:50.641 --> 00:02:52.162
So eight and seven fifths,

00:02:52.162 --> 00:02:55.807
this is the same thing as eight plus,

00:02:55.807 --> 00:02:57.560
and instead of seven fifths,

00:02:57.560 --> 00:03:00.045
we could say this is the
same thing as five fifths,

00:03:00.045 --> 00:03:02.877
which is a whole, plus two fifths.

00:03:03.737 --> 00:03:06.708
Now why is that interesting?

00:03:06.708 --> 00:03:08.589
Because five fifths, notice
five fifths plus two fifths,

00:03:08.589 --> 00:03:10.330
that's seven fifths right over there.

00:03:10.330 --> 00:03:12.756
Or you can consider five fifths to be one,

00:03:12.756 --> 00:03:15.508
so this is eight plus one, which is nine,

00:03:15.508 --> 00:03:19.995
and two fifths, nine and two fifths.

00:03:20.012 --> 00:03:22.055
So all I did here, I added it the same way

00:03:22.055 --> 00:03:25.004
that I did the first
problem a few seconds ago.

00:03:25.004 --> 00:03:28.626
But when I realize this fraction
part is greater than one,

00:03:28.626 --> 00:03:31.273
I separated it into
one and then a fraction

00:03:31.273 --> 00:03:32.527
that is less than one,

00:03:32.527 --> 00:03:34.547
and that whole, I was able to add

00:03:34.547 --> 00:03:36.009
to the eight to get to nine,

00:03:36.009 --> 00:03:38.087
and then I would have
two fifths left over.

00:03:38.087 --> 00:03:40.804
Eight and seven fifths,
because five fifths is a whole,

00:03:40.804 --> 00:03:43.474
is the same thing as nine and two fifths.

00:03:43.474 --> 00:03:46.933
So if I wanted to write this
in, I guess, a clearer way,

00:03:46.933 --> 00:03:48.442
I would say this is nine and two fifths.

00:03:48.442 --> 00:03:50.242
Three and three fifths
plus five and four fifths

00:03:50.242 --> 00:03:51.751
is nine and two fifths,

00:03:51.751 --> 00:03:53.504
and once again, we say wait,
three plus five is only eight,

00:03:53.504 --> 00:03:54.630
how did I get a nine?

00:03:54.630 --> 00:03:56.929
Well that's because three
fifths plus four fifths

00:03:56.929 --> 00:03:59.361
is greater than one.


Subtracting mixed numbers introduction

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:01.290
- [Voiceover] Let's get some practice

00:00:01.290 --> 00:00:02.775
subtracting mixed numbers.

00:00:02.775 --> 00:00:06.791
So let's say that I had 2 5/8

00:00:06.791 --> 00:00:11.791
minus 1 2/8.

00:00:13.606 --> 00:00:15.788
What is this going to be?

00:00:15.788 --> 00:00:16.984
I encourage you to pause the video

00:00:16.984 --> 00:00:18.167
and try to work it out.

00:00:18.167 --> 00:00:20.502
Well, we can rewrite this, we could write

00:00:20.502 --> 00:00:21.663
the numbers on top of each other,

00:00:21.663 --> 00:00:24.797
we could say this is two,
in that magenta color,

00:00:24.797 --> 00:00:27.955
say this is 2 5/8,

00:00:27.955 --> 00:00:30.612
actually let me write it a
little bit further spaced apart,

00:00:30.612 --> 00:00:33.976
2 5/8,

00:00:33.976 --> 00:00:38.492
minus 1 2/8.

00:00:39.403 --> 00:00:41.816
And then, we can subtract.

00:00:41.816 --> 00:00:43.531
We could say, okay look, in this column

00:00:43.531 --> 00:00:45.704
right over here, we are
subtracting eighths.

00:00:45.704 --> 00:00:47.887
We have five eighths, and we're gonna

00:00:47.887 --> 00:00:49.047
subtract two eighths.

00:00:49.047 --> 00:00:50.208
If I have five of something
and I'm gonna subtract

00:00:50.208 --> 00:00:52.943
two of them, I'm gonna have
three of that something,

00:00:52.943 --> 00:00:54.144
and in this case we're
talking about eighths.

00:00:54.144 --> 00:00:55.583
So five eighths minus two eighths

00:00:55.583 --> 00:00:57.500
is going to be three eighths,

00:00:57.500 --> 00:01:00.137
and then you have two ones minus one one,

00:01:00.137 --> 00:01:02.875
or two minus one, is going to be one.

00:01:02.875 --> 00:01:07.875
So this is going to be equal
to one and three eighths.

00:01:08.160 --> 00:01:10.216
Now let's do something more interesting.

00:01:10.216 --> 00:01:12.933
Let's say that we had 3, I'm just going

00:01:12.933 --> 00:01:17.933
to make up a number here, 3 2/5

00:01:18.993 --> 00:01:23.993
minus 2 3/5,

00:01:25.056 --> 00:01:28.202
and like always, pause the
video and try to work it out.

00:01:28.202 --> 00:01:31.186
Let's try to work it
out this exact same way.

00:01:31.186 --> 00:01:33.657
So I'm going to rewrite it as 3,

00:01:33.657 --> 00:01:37.341
let me do that same magenta
color, changing colors,

00:01:37.341 --> 00:01:41.879
we have three and two over five

00:01:41.879 --> 00:01:46.879
minus two and three over five.

00:01:48.056 --> 00:01:50.262
Two and three over five.

00:01:50.262 --> 00:01:51.979
And when you first try to do it,

00:01:51.979 --> 00:01:53.734
over here you had 5/8 minus 2/8,

00:01:53.734 --> 00:01:56.384
that was easy to figure out, that's 3/8.

00:01:56.384 --> 00:02:00.209
But then over here,
you have 2/5 minus 3/5.

00:02:00.209 --> 00:02:01.346
Well, that's hard!

00:02:01.346 --> 00:02:03.413
3/5 is larger than 2/5.

00:02:03.413 --> 00:02:05.410
So what can you do here?

00:02:05.410 --> 00:02:07.964
Well one option is to regroup.

00:02:07.964 --> 00:02:10.343
Let's take one, from I guess you could say

00:02:10.343 --> 00:02:13.651
the ones place, here, so
let's take one from this,

00:02:13.651 --> 00:02:15.811
and then that's going to turn into two.

00:02:15.811 --> 00:02:18.795
And then one is the same thing as 5/5.

00:02:18.795 --> 00:02:23.694
So two plus 5/5 is equal to 7/5.

00:02:23.694 --> 00:02:25.436
So another way of thinking about it,

00:02:25.436 --> 00:02:28.861
I'll do it over here, we could write,

00:02:28.861 --> 00:02:32.932
3 2/5 is the same thing as 2 7/5.

00:02:32.932 --> 00:02:37.932
2 7/5. These two things are equivalent.

00:02:38.550 --> 00:02:41.753
Why? Well I took one away
from here to get to two,

00:02:41.753 --> 00:02:43.913
and then I added that one over here.

00:02:43.913 --> 00:02:46.236
One is same thing as 5/5.

00:02:46.236 --> 00:02:48.337
2/5 plus 5/5 is 7/5.

00:02:48.337 --> 00:02:53.050
So now if we consider
this thing to be 2 7/5,

00:02:53.050 --> 00:02:55.035
we're ready to subtract.

00:02:55.035 --> 00:03:00.035
If you say 7/5 minus 3/5,

00:03:00.201 --> 00:03:04.033
that's going to be 4/5.

00:03:04.033 --> 00:03:06.120
And then you have two
minus two is zero ones,

00:03:06.120 --> 00:03:08.581
so you're just going to be left with 4/5.

00:03:08.581 --> 00:03:11.321
So this is just going to be 4/5.

00:03:11.321 --> 00:03:12.923
Let's do that again.

00:03:12.923 --> 00:03:14.816
Let's do one where we
have to regroup again.

00:03:14.816 --> 00:03:16.742
And I'll just write it out in a column,

00:03:16.742 --> 00:03:18.472
up down, to begin with.

00:03:18.472 --> 00:03:21.049
Let's say that we have

00:03:21.049 --> 00:03:26.049
7 1/6, minus

00:03:28.309 --> 00:03:32.117
4 5/6.

00:03:35.487 --> 00:03:37.714
What is this going to be equal to?

00:03:37.714 --> 00:03:40.616
Well, when we try to
subtract 5/6 from 1/6,

00:03:40.616 --> 00:03:43.158
well that's hard, 5/6 is larger than 1/6.

00:03:43.158 --> 00:03:44.656
But we can regroup.

00:03:44.656 --> 00:03:46.455
We could take one from here, so the seven

00:03:46.455 --> 00:03:48.974
becomes a six.

00:03:48.974 --> 00:03:51.238
And then we take that one, which is

00:03:51.238 --> 00:03:54.292
the same thing as 6/6, and add it to 1/6.

00:03:54.292 --> 00:03:59.292
So 1/6 plus 6/6, is going to be 7/6.

00:04:02.514 --> 00:04:03.793
Let me be clear what I did.

00:04:03.793 --> 00:04:06.370
I took one from the
seven, and it became six,

00:04:06.370 --> 00:04:11.025
and one is equal to 6/6, and so I added

00:04:11.025 --> 00:04:13.963
6/6 to that 1/6, and I got 7/6.

00:04:13.963 --> 00:04:16.586
So I took the one from here,
and I added it over here,

00:04:16.586 --> 00:04:21.113
and the whole purpose is,
now 7/6 is greater than 5/6.

00:04:21.733 --> 00:04:26.733
So 7/6 minus 5/6 is, I'll
do that orange color,

00:04:26.966 --> 00:04:29.956
is 2/6,

00:04:29.956 --> 00:04:34.246
and six minus four is two.

00:04:34.404 --> 00:04:36.342
So it's gonna be 2 2/6, or, if we wanted

00:04:36.342 --> 00:04:39.988
to rewrite 2/6, you see
they're both divisible by two,

00:04:39.988 --> 00:04:44.545
this is the same thing as 2
and 1/3 is equivalent to 2/6.

00:04:44.545 --> 00:04:47.743
So you could also write it like that.


Phases of meiosis II

WEBVTT
Kind: captions
Language: en

00:00:00.329 --> 00:00:03.394
- [Voiceover] In the last video,
we had completed meiosis I,

00:00:03.394 --> 00:00:06.482
and now we're ready to go into meiosis II.

00:00:06.482 --> 00:00:07.527
And you might be wondering,

00:00:07.527 --> 00:00:11.428
"Well, hey, after mitosis, we
went back into our interphase,

00:00:11.428 --> 00:00:13.053
"is there kind of a rest period

00:00:13.053 --> 00:00:15.630
"between our two phases of meiosis?"

00:00:15.630 --> 00:00:17.999
And the answer is, sometimes.

00:00:17.999 --> 00:00:19.926
There can be a rest period

00:00:19.926 --> 00:00:22.526
where you have an interphase II,

00:00:22.526 --> 00:00:24.477
and that will depend on the type of cell

00:00:24.477 --> 00:00:25.939
and the species and all of that,

00:00:25.939 --> 00:00:27.309
but it is possible,

00:00:27.309 --> 00:00:30.049
so I'll actually put that over here.

00:00:30.049 --> 00:00:33.018
So we could have an interphase II.

00:00:33.671 --> 00:00:35.386
So interphase...

00:00:36.852 --> 00:00:38.803
interphase II,

00:00:38.803 --> 00:00:39.941
which you could kind of view

00:00:39.941 --> 00:00:42.588
as a rest period.

00:00:42.588 --> 00:00:45.769
But then we get into meiosis II,

00:00:45.769 --> 00:00:49.042
which will allow us to
complete all of meiosis.

00:00:49.042 --> 00:00:51.039
So you can imagine meiosis II

00:00:51.039 --> 00:00:53.454
starts with prophase II.

00:00:53.454 --> 00:00:54.499
And in prophase II,

00:00:54.499 --> 00:00:56.774
now I'm dealing with two cells here,

00:00:56.774 --> 00:00:57.889
so in prophase II,

00:00:57.889 --> 00:01:00.304
and I'm gonna do it for both of the cells

00:01:00.304 --> 00:01:03.415
that I have after I finished meiosis I,

00:01:03.415 --> 00:01:05.481
so in prophase II,

00:01:05.481 --> 00:01:07.807
so let me...

00:01:08.571 --> 00:01:09.722
that's one of the cells.

00:01:09.722 --> 00:01:11.742
I'm not gonna have space
to draw it properly,

00:01:11.742 --> 00:01:13.182
so let me draw it,

00:01:13.182 --> 00:01:15.086
so let me draw this one first.

00:01:15.086 --> 00:01:17.640
So this is one of the cells

00:01:17.640 --> 00:01:18.638
right over here,

00:01:18.638 --> 00:01:22.423
and then this is the other cell

00:01:22.423 --> 00:01:24.187
right over here.

00:01:24.187 --> 00:01:25.952
In prophase II,

00:01:25.952 --> 00:01:27.577
just like in prophase I,

00:01:27.577 --> 00:01:29.528
and just like in prophase in mitosis,

00:01:29.528 --> 00:01:31.107
and let me write the phases here,

00:01:31.107 --> 00:01:33.312
this is prophase II we're talking about,

00:01:33.312 --> 00:01:37.027
prophase II.

00:01:37.027 --> 00:01:39.883
Your nuclear envelope dissolves again,

00:01:39.883 --> 00:01:44.434
so let me show a dissolving
nuclear envelope.

00:01:44.434 --> 00:01:48.382
So your nuclear envelope dissolves again,

00:01:48.382 --> 00:01:52.352
and your chromosomes

00:01:52.352 --> 00:01:54.256
once again condensing (mumbles)

00:01:54.256 --> 00:01:56.392
I guess you could say
into their denser form,

00:01:56.392 --> 00:02:00.850
so it's gonna look like this,

00:02:00.850 --> 00:02:02.917
this, and this.

00:02:02.917 --> 00:02:06.446
On this side, it has a
little bit of the magenta

00:02:06.446 --> 00:02:08.211
that was from the chromosomal crossover

00:02:08.211 --> 00:02:10.022
back in prophase I,

00:02:10.022 --> 00:02:12.553
and then you have this
character right over here

00:02:12.553 --> 00:02:13.992
that is shorter.

00:02:13.992 --> 00:02:18.172
You have this chromosome,

00:02:18.172 --> 00:02:19.356
right over here,

00:02:19.356 --> 00:02:20.981
and it had a little orange section

00:02:20.981 --> 00:02:23.814
from the chromosomal
crossover just like this,

00:02:23.814 --> 00:02:26.972
and then you have the
shorter orange chromosome

00:02:26.972 --> 00:02:27.575
just like that,

00:02:27.575 --> 00:02:29.108
so they have condensed,

00:02:29.108 --> 00:02:30.810
and you've actually,

00:02:30.810 --> 00:02:32.005
each of these cells now

00:02:32.005 --> 00:02:35.628
will have duplicate centrosomes.

00:02:35.628 --> 00:02:37.833
So the centrosomes have replicated

00:02:37.833 --> 00:02:40.488
and they will start

00:02:40.488 --> 00:02:44.319
to migrate to opposite ends

00:02:44.319 --> 00:02:45.620
of the cell.

00:02:45.620 --> 00:02:48.801
So once again, very strong analogy,

00:02:48.801 --> 00:02:52.330
especially to frankly,
prophase from mitosis.

00:02:52.330 --> 00:02:53.909
So now let's keep going.

00:02:53.909 --> 00:02:56.904
We're now ready to go to metaphase II.

00:02:56.904 --> 00:02:58.594
Metaphase II.

00:02:59.737 --> 00:03:03.466
Metaphase II.

00:03:03.847 --> 00:03:06.066
And let me draw my two cells.

00:03:06.066 --> 00:03:09.148
This is one of them

00:03:10.083 --> 00:03:11.996
and then this is...

00:03:11.996 --> 00:03:13.273
the other.

00:03:13.273 --> 00:03:14.365
Let me draw an arrow here

00:03:14.365 --> 00:03:17.148
so you can see that we are entering

00:03:17.148 --> 00:03:18.928
into another phase.

00:03:20.121 --> 00:03:22.347
So we are entering into another phase.

00:03:22.347 --> 00:03:23.740
Metaphase II.

00:03:23.740 --> 00:03:25.272
And you can just imagine,

00:03:25.272 --> 00:03:27.524
it's very similar to what
happens in metaphase in mitosis.

00:03:27.524 --> 00:03:29.312
And actually all of meiosis II

00:03:29.312 --> 00:03:33.027
is very similar to what
happens in mitosis.

00:03:33.027 --> 00:03:34.374
So in metaphase II,

00:03:34.374 --> 00:03:39.374
our centrosomes have
migrated to the poles.

00:03:39.645 --> 00:03:41.409
So our centrosomes

00:03:41.409 --> 00:03:44.498
have migrated to the poles.

00:03:44.498 --> 00:03:45.357
And I'm gonna do it twice,

00:03:45.357 --> 00:03:46.285
because I'm now dealing with

00:03:46.285 --> 00:03:49.181
two different cells.

00:03:49.181 --> 00:03:52.787
My nuclear membrane is now disappeared.

00:03:52.787 --> 00:03:55.294
And I have my now dense chromosomes

00:03:55.294 --> 00:03:58.104
lining up along the equator here.

00:03:58.104 --> 00:04:00.797
So this magenta one,

00:04:00.797 --> 00:04:03.816
it'll line up here over here.

00:04:03.816 --> 00:04:05.906
So it might look like that.

00:04:05.906 --> 00:04:07.554
And actually, let me draw
all the magenta ones now

00:04:07.554 --> 00:04:11.199
since I have my magenta color selected.

00:04:11.199 --> 00:04:13.359
So this is the longer one in this one.

00:04:13.359 --> 00:04:16.749
And this had a little bit of orange in it.

00:04:16.749 --> 00:04:19.907
Let me, has a little
bit of the orange here,

00:04:19.907 --> 00:04:24.063
and then I had the
shorter orange chromosome.

00:04:24.063 --> 00:04:25.781
The shorter orange chromosome on this cell

00:04:25.781 --> 00:04:29.769
had the longer, the
larger orange chromosome.

00:04:30.912 --> 00:04:34.163
So then it had a little bit of pink on it.

00:04:34.163 --> 00:04:37.901
And of course, you have your
microtubules, that are...

00:04:37.901 --> 00:04:39.387
I've been doing that in blue,

00:04:39.387 --> 00:04:41.082
so I'm gonna continue to do it in blue,

00:04:41.082 --> 00:04:45.238
that are pushing the centrosomes apart,

00:04:45.238 --> 00:04:48.331
but are also attaching to the chromosomes

00:04:49.101 --> 00:04:51.303
at the kinetochores.

00:04:51.303 --> 00:04:53.439
At the kinetochores.

00:04:53.439 --> 00:04:54.205
So there you go,

00:04:54.205 --> 00:04:55.320
and remember this right over here,

00:04:55.320 --> 00:04:57.409
where the two sister chromotids attached,

00:04:57.409 --> 00:05:01.078
those are our centromeres.

00:05:01.078 --> 00:05:04.514
So let me just draw it all out like this.

00:05:04.514 --> 00:05:05.582
So it might go,

00:05:05.582 --> 00:05:07.626
it might be something like that.

00:05:07.626 --> 00:05:10.087
And now we're ready to anaphase II,

00:05:10.087 --> 00:05:11.805
and you can imagine
what's about to happen.

00:05:11.805 --> 00:05:13.918
Things are about to pull apart.

00:05:13.918 --> 00:05:15.474
And once again, this is analogous

00:05:15.474 --> 00:05:18.237
to what happens in anaphase in mitosis,

00:05:18.237 --> 00:05:19.235
so let me...

00:05:19.235 --> 00:05:20.925
So anaphase II.

00:05:22.230 --> 00:05:25.435
Anaphase II.

00:05:25.435 --> 00:05:26.897
I'm gonna draw all my cells again,

00:05:26.897 --> 00:05:27.919
this is taking me twice as long

00:05:27.919 --> 00:05:30.404
because I have to do it
for twice as many cells,

00:05:30.404 --> 00:05:32.609
so that's one cell there.

00:05:32.609 --> 00:05:35.512
This is another cell here,

00:05:35.512 --> 00:05:38.786
this is, I got a centrosome here,

00:05:38.786 --> 00:05:41.107
centrosome here, centrosome here,

00:05:41.107 --> 00:05:42.779
centrosome here,

00:05:42.779 --> 00:05:43.638
and then the key here

00:05:43.638 --> 00:05:45.333
is this is why it's like mitosis

00:05:45.333 --> 00:05:48.584
and not like anaphase in meiosis I,

00:05:48.584 --> 00:05:51.277
is instead of, or like in mitosis,

00:05:51.277 --> 00:05:53.669
we're now going to split
the sister chromatids

00:05:53.669 --> 00:05:56.107
so they now become two
daughter chromosomes.

00:05:56.107 --> 00:05:57.918
When they're connected,
they're just together,

00:05:57.918 --> 00:05:59.706
they're viewed as sister chromatids

00:05:59.706 --> 00:06:01.145
that make up one chromosome,

00:06:01.145 --> 00:06:04.443
but now they get, now
they're getting pulled apart.

00:06:04.443 --> 00:06:07.415
So this one might get pulled

00:06:07.415 --> 00:06:09.249
in this direction,

00:06:09.249 --> 00:06:11.687
and then this one

00:06:11.687 --> 00:06:13.219
might get pulled

00:06:13.219 --> 00:06:14.032
in this direction.

00:06:14.032 --> 00:06:17.190
It has a little bit of the
magenta right over here

00:06:17.190 --> 00:06:20.673
and then one of the sister chromatids,

00:06:20.673 --> 00:06:22.344
which would now be a daughter chromosome,

00:06:22.344 --> 00:06:24.573
going in upwards in one of them,

00:06:24.573 --> 00:06:26.245
going downwards.

00:06:26.245 --> 00:06:29.908
And let me draw all the microtubules here.

00:06:30.541 --> 00:06:32.886
All the microtubules that are doing,

00:06:32.886 --> 00:06:35.254
that are super involved
in all of this work

00:06:35.254 --> 00:06:37.669
of getting things to the
right sides of cells,

00:06:37.669 --> 00:06:39.968
and this is gonna happen
in this cell as well.

00:06:39.968 --> 00:06:41.988
So in this cell,

00:06:41.988 --> 00:06:44.054
so this one...

00:06:44.054 --> 00:06:47.305
might be going down here,

00:06:47.305 --> 00:06:49.441
and this one

00:06:49.441 --> 00:06:51.415
is moving up here,

00:06:51.415 --> 00:06:53.992
and this one had a little chunk

00:06:53.992 --> 00:06:55.894
of orange on it,

00:06:55.894 --> 00:06:57.613
so let me draw that.

00:06:57.613 --> 00:06:58.936
Little chunk of orange.

00:06:58.936 --> 00:07:00.538
And then once again,

00:07:00.538 --> 00:07:03.325
one of the formerly sister chromatids,

00:07:03.325 --> 00:07:05.600
now daughter chromosomes going up there,

00:07:05.600 --> 00:07:08.776
and now going down over here.

00:07:09.756 --> 00:07:10.487
Over here.

00:07:10.487 --> 00:07:13.529
And let me draw the microtubules

00:07:14.789 --> 00:07:16.275
that are really...

00:07:16.275 --> 00:07:18.063
well, I've said it multiple times,

00:07:18.063 --> 00:07:21.197
super involved in actual
the movement going on.

00:07:21.197 --> 00:07:23.310
They're elongating, they're
these motor proteins

00:07:23.310 --> 00:07:26.398
that are moving the chromosomes along,

00:07:26.398 --> 00:07:28.674
once again, they're
connected at the kinetochores

00:07:28.674 --> 00:07:30.322
right over here.

00:07:30.322 --> 00:07:32.853
Connected at the kinetochores.

00:07:32.853 --> 00:07:34.386
Right over there.

00:07:34.386 --> 00:07:36.081
And now we're almost done,

00:07:36.081 --> 00:07:39.169
we're ready to move into telophase II.

00:07:39.169 --> 00:07:43.436
So we're now going to
go into telophase II.

00:07:44.672 --> 00:07:48.103
Telophase II.

00:07:48.805 --> 00:07:52.450
Where my two cells are
now becoming four cells,

00:07:52.450 --> 00:07:53.750
so telophase II,

00:07:53.750 --> 00:07:57.074
I'm gonna show the cytokinesis
starting to happen.

00:07:58.324 --> 00:08:00.399
So telophase II.

00:08:00.399 --> 00:08:05.061
So turning into four cells,

00:08:05.062 --> 00:08:08.661
trying to show the
cytokinesis happening on...

00:08:08.661 --> 00:08:12.678
In this cell up here,
I have this character,

00:08:12.678 --> 00:08:15.519
and has a little bit of
magenta right over here.

00:08:16.439 --> 00:08:17.438
That's this right over there

00:08:17.438 --> 00:08:19.628
and then you have the shorter magenta one.

00:08:19.636 --> 00:08:21.166
And actually, they are starting to,

00:08:21.166 --> 00:08:23.302
they're starting to unravel
into their chromatid form,

00:08:23.302 --> 00:08:25.160
so maybe I'll draw that a little bit,

00:08:25.160 --> 00:08:27.482
and then this one, right over here,

00:08:27.482 --> 00:08:30.732
is starting to unravel
into its chromatid form.

00:08:30.732 --> 00:08:33.867
And so it this that one.

00:08:33.867 --> 00:08:36.746
Whoops, wanna do that
in that magenta color.

00:08:36.746 --> 00:08:39.138
Starting to unravel
into its chromatid form,

00:08:39.138 --> 00:08:40.136
I wanna do it over here,

00:08:40.136 --> 00:08:43.131
this one is starting to unravel.

00:08:43.131 --> 00:08:45.155
And so is this one.

00:08:46.196 --> 00:08:48.430
So is...

00:08:50.601 --> 00:08:52.359
(laughs) I'm having
trouble changing colors.

00:08:52.359 --> 00:08:54.078
And so is that one,

00:08:54.078 --> 00:08:55.076
and then up here,

00:08:55.076 --> 00:08:56.260
this one's starting to unravel,

00:08:56.260 --> 00:08:57.328
this one over here,

00:08:57.328 --> 00:08:58.346
and...

00:08:58.907 --> 00:09:01.345
this longer, mostly magenta one

00:09:01.345 --> 00:09:03.368
is also starting to unravel.

00:09:03.368 --> 00:09:05.040
Also starting to unravel.

00:09:05.040 --> 00:09:08.198
You start having your nuclear
envelope formed again,

00:09:08.198 --> 00:09:11.513
so your nuclear envelope is forming again.

00:09:12.610 --> 00:09:16.714
Nuclear envelope is forming.

00:09:17.346 --> 00:09:20.225
Your microtubules are dissolving.

00:09:20.225 --> 00:09:22.246
Let me draw the centrosomes,

00:09:22.246 --> 00:09:24.005
they're outside of the nuclear envelope.

00:09:24.730 --> 00:09:26.564
Outside of the nuclear envelope.

00:09:26.564 --> 00:09:29.652
And of course, you're
finally dividing the cells,

00:09:29.652 --> 00:09:30.906
your cytokinesis happens,

00:09:30.906 --> 00:09:33.716
so now you have your four,

00:09:33.716 --> 00:09:35.620
your four cells,

00:09:35.620 --> 00:09:37.524
each have a haploid number.

00:09:37.524 --> 00:09:39.056
They each have two chromosomes.

00:09:39.056 --> 00:09:41.610
Remember, you diploid number was four,

00:09:41.610 --> 00:09:43.189
the germ cell had four chromosomes,

00:09:43.189 --> 00:09:46.440
two pairs of homologous chromosomes.

00:09:46.440 --> 00:09:50.224
Now each of your resulting gametes,

00:09:50.224 --> 00:09:52.430
these are now gametes now,

00:09:52.430 --> 00:09:55.263
these are gametes,

00:09:55.263 --> 00:09:56.331
they have a haploid number.

00:09:56.331 --> 00:09:57.631
But we started with a haploid number

00:09:57.631 --> 00:09:59.651
at the beginning of meiosis II,

00:09:59.651 --> 00:10:01.509
so that's why meiosis II

00:10:01.509 --> 00:10:03.738
is often compared to mitosis.

00:10:03.738 --> 00:10:04.690
So let me make this clear.

00:10:04.690 --> 00:10:07.174
This right over here is meiosis II

00:10:07.174 --> 00:10:10.657
because it preserves the
number of chromosomes,

00:10:10.657 --> 00:10:11.702
just like mitosis.

00:10:11.702 --> 00:10:14.413
So this is meisosis,

00:10:15.440 --> 00:10:17.507
meiosis II right over here.

00:10:18.207 --> 00:10:19.614
We started with a haploid number

00:10:19.614 --> 00:10:22.099
and we finished with a haploid number

00:10:22.099 --> 00:10:23.143
just like this,

00:10:23.143 --> 00:10:24.328
and now these gametes

00:10:24.328 --> 00:10:27.392
are ready for some fertilization.

00:10:27.392 --> 00:10:28.577
And it's important to realize now,

00:10:28.577 --> 00:10:30.666
now these each have two chromosomes,

00:10:30.666 --> 00:10:34.196
and these are not homologous chromosomes.

00:10:34.196 --> 00:10:36.935
These are coding for different genes.

00:10:36.935 --> 00:10:38.329
But then they will each of these

00:10:38.329 --> 00:10:40.859
have the potential to fuse with,

00:10:40.859 --> 00:10:43.088
if this is a sperm cell,

00:10:43.088 --> 00:10:44.366
then this could fuse with an egg

00:10:44.366 --> 00:10:46.687
and then together they can create

00:10:46.687 --> 00:10:48.963
a diploid number of chromosomes.

00:10:48.963 --> 00:10:52.260
It could have the full
complement of homologous pairs.

00:10:52.260 --> 00:10:53.258
But that's what these are for,

00:10:53.258 --> 00:10:56.202
these are for sexual reproduction.


Phases of meiosis I

WEBVTT
Kind: captions
Language: en

00:00:00.385 --> 00:00:01.557
- [Voiceover] In the last video,

00:00:01.557 --> 00:00:04.459
we had just started to get into meiosis,

00:00:04.459 --> 00:00:06.398
and to be more precise, meiosis I,

00:00:06.398 --> 00:00:08.964
and to be even more precise
than that, prophase I,

00:00:08.964 --> 00:00:11.018
but we spent a good bit
of time on prophase I

00:00:11.018 --> 00:00:12.783
because some interesting things happened.

00:00:12.783 --> 00:00:15.198
Some things happened just
like prophase in mitosis where

00:00:15.198 --> 00:00:19.226
the nuclear envelope disappears
or starts to disappear,

00:00:19.226 --> 00:00:23.022
you have the chromosomes
going into their dense form

00:00:23.022 --> 00:00:24.705
that has kinda this classic shape that you

00:00:24.705 --> 00:00:26.505
could see from a microscope,

00:00:26.505 --> 00:00:29.395
but what was unique or
what was interesting

00:00:29.395 --> 00:00:32.820
about meiosis I and
prophase I in particular

00:00:32.820 --> 00:00:35.479
is that you have this
chromosomal crossover,

00:00:35.479 --> 00:00:39.484
that is a pretty typical
thing to happen in meiosis I,

00:00:39.484 --> 00:00:43.303
and it tends to happen
in a fairly clean way

00:00:43.303 --> 00:00:47.238
where homologous sections
of these homologous pairs

00:00:47.238 --> 00:00:51.329
crossover, so these
sections of the chromosome

00:00:51.329 --> 00:00:54.139
tend to code for the same genes.

00:00:54.139 --> 00:00:55.892
They're just different
variants of those same genes.

00:00:55.892 --> 00:00:57.343
They might have different alleles,

00:00:57.343 --> 00:00:59.653
and then once again, this
just adds more variation

00:00:59.653 --> 00:01:02.277
as we get into sexual reproduction,

00:01:02.277 --> 00:01:04.970
so it's a kind of neat
thing that happens here.

00:01:04.970 --> 00:01:07.036
But now let's continue with meiosis,

00:01:07.036 --> 00:01:09.718
and in particular meiosis
I, and you could guess

00:01:09.718 --> 00:01:11.993
what the next phase is going to be called.

00:01:11.993 --> 00:01:16.993
It is metaphase I, metaphase, metaphase I,

00:01:17.554 --> 00:01:21.814
and it has some similarities
with metaphase in mitosis.

00:01:21.814 --> 00:01:24.943
So in metaphase I, let me draw my cell,

00:01:25.727 --> 00:01:30.231
so this is the cellular
membrane right over there.

00:01:30.231 --> 00:01:32.413
I have my centrosomes,
which are now going to play

00:01:32.413 --> 00:01:34.800
more significant roles.

00:01:35.153 --> 00:01:38.032
The nuclear membrane is now gone,

00:01:38.032 --> 00:01:41.527
and just like in metaphase in mitosis,

00:01:41.527 --> 00:01:43.674
my chromosomes are going to line up

00:01:43.674 --> 00:01:48.225
along the, here I'll draw it,
kind of this up, down axis.

00:01:48.225 --> 00:01:49.595
So let's do that.

00:01:49.595 --> 00:01:52.956
So you have this one right over here.

00:01:53.774 --> 00:01:57.182
This is one chromosome,
two sister chromatids,

00:01:57.245 --> 00:01:58.905
and we had the chromosomal crossover,

00:01:58.905 --> 00:02:00.507
so it has a little bit of pink here.

00:02:00.507 --> 00:02:01.285
I'm gonna take a little bit of time

00:02:01.285 --> 00:02:03.189
to switch colors a little
bit more frequently.

00:02:03.189 --> 00:02:05.685
And then you have the one,
at least most of which

00:02:05.685 --> 00:02:07.792
you got from your mother,

00:02:07.972 --> 00:02:09.063
yeah but there's been a little bit

00:02:09.063 --> 00:02:12.134
of chromosomal crossover here as well.

00:02:12.290 --> 00:02:14.096
So let me draw that.

00:02:14.403 --> 00:02:15.587
Let me draw that.

00:02:15.587 --> 00:02:17.004
And then you have this one,

00:02:17.004 --> 00:02:19.082
and just for the sake of,

00:02:19.082 --> 00:02:23.221
so you have this one, this
chromosome from your father.

00:02:23.621 --> 00:02:26.692
It has replicated, so it's
now two sister chromatids.

00:02:26.720 --> 00:02:27.661
And this one from your mother,

00:02:27.661 --> 00:02:30.226
and I'm not gonna show the
chromosomal crossover here.

00:02:30.226 --> 00:02:32.171
Maybe it didn't happen over here.

00:02:32.525 --> 00:02:34.818
No homologous recombination over here.

00:02:35.311 --> 00:02:37.360
So these are, I guess, shorter.

00:02:38.248 --> 00:02:40.379
Now let me draw the centromeres.

00:02:40.605 --> 00:02:43.095
The centromeres I started
doing in this blue color.

00:02:43.449 --> 00:02:47.442
So the centromeres, the centromeres,

00:02:47.442 --> 00:02:48.824
and then the centrosomes,

00:02:48.824 --> 00:02:51.262
you have these microtubules that start,

00:02:51.262 --> 00:02:54.303
they can push the centrosomes
away from each other.

00:02:54.303 --> 00:02:58.529
But they also attach at the
kinetochores to the chromosomes,

00:02:58.529 --> 00:03:01.629
to the chromosomes, just like that.

00:03:01.629 --> 00:03:05.146
And these are, the microtubules,
you'll see people talk

00:03:05.146 --> 00:03:07.398
about oh these connect, and they're able

00:03:07.398 --> 00:03:08.223
to move things around,

00:03:08.223 --> 00:03:10.579
but I find this incredible
that you just have

00:03:10.579 --> 00:03:13.447
a bunch of proteins through
just kind of chemical

00:03:13.447 --> 00:03:17.986
and thermodynamic processes,

00:03:17.986 --> 00:03:19.901
are able to do really interesting things

00:03:19.901 --> 00:03:24.684
like move chromosomes to
different parts of the cell,

00:03:24.684 --> 00:03:27.401
so that we eventually can
get these gametes that can

00:03:27.401 --> 00:03:30.965
participate in sexual reproduction.

00:03:30.965 --> 00:03:32.300
This is an amazing thing,

00:03:32.300 --> 00:03:37.300
and it's developed over
billions of years of evolution,

00:03:38.325 --> 00:03:41.157
but it's just mind boggling
to think about the complexity,

00:03:41.157 --> 00:03:42.504
and not all of this is
completely understood

00:03:42.504 --> 00:03:43.874
exactly how all of this works.

00:03:43.874 --> 00:03:45.836
I mean you have these
kind of motor proteins

00:03:45.836 --> 00:03:50.836
that help move the chromosomes
along, these microtubules

00:03:51.199 --> 00:03:53.753
can elongate and shorten
in interesting ways.

00:03:53.753 --> 00:03:55.761
So it's a really fascinating process.

00:03:55.761 --> 00:03:58.733
But anyway, this is what's
happening in metaphase I.

00:03:58.733 --> 00:04:01.252
Now you can probably guess
what happens after that.

00:04:01.252 --> 00:04:03.632
We then move to anaphase I.

00:04:03.632 --> 00:04:06.581
So let me, we now go to anaphase I.

00:04:06.581 --> 00:04:08.004
I'll write that over here.

00:04:08.113 --> 00:04:11.533
Anaphase, anaphase I,

00:04:12.014 --> 00:04:14.881
and just like anaphase in mitosis,

00:04:14.881 --> 00:04:19.072
over here, the chromosomes
start getting pulled apart,

00:04:19.072 --> 00:04:21.893
except for one significant difference,

00:04:21.893 --> 00:04:24.349
and this is actually a very
significant difference.

00:04:24.378 --> 00:04:29.378
In mitosis, the sister
chromatids get pulled apart.

00:04:30.159 --> 00:04:32.121
The sister chromatids get pulled apart

00:04:32.121 --> 00:04:34.779
to become two daughter chromosomes.

00:04:34.779 --> 00:04:37.554
That does not happen in anaphase I.

00:04:37.554 --> 00:04:41.849
In anaphase I, the sister
chromatids stay together.

00:04:41.849 --> 00:04:45.942
It's the homologous pairs
that get pulled apart.

00:04:45.970 --> 00:04:47.370
So let me draw that.

00:04:47.549 --> 00:04:49.952
So this homologous pair
up here gets pulled apart.

00:04:49.952 --> 00:04:52.959
The two sister chromatids do
not get pulled apart here.

00:04:52.959 --> 00:04:56.901
So you have this one is
getting pulled onto this side.

00:04:57.533 --> 00:05:00.017
So this one's getting
pulled onto this side.

00:05:00.017 --> 00:05:03.395
It has a little bit from the original,

00:05:03.395 --> 00:05:06.037
so a little bit of that right over there.

00:05:06.077 --> 00:05:09.102
And then you have this one
getting pulled on this side.

00:05:09.548 --> 00:05:14.517
So draw it the best I can, the colors,

00:05:14.517 --> 00:05:15.515
alright, so it looks like that,

00:05:15.515 --> 00:05:17.628
although it's nice to have,
it's kinda easy to keep track of

00:05:17.628 --> 00:05:19.787
cause these switch colors like that.

00:05:19.787 --> 00:05:22.824
And then you have this one
getting pulled on this side.

00:05:23.375 --> 00:05:25.035
This one getting pulled on this side.

00:05:25.035 --> 00:05:30.035
And finally finally this one
getting pulled onto that side.

00:05:32.372 --> 00:05:34.728
And let me draw the centrosomes.

00:05:34.728 --> 00:05:37.410
So that's my, oops, centrosome,

00:05:37.410 --> 00:05:39.290
and once again, it's pulling,

00:05:39.290 --> 00:05:41.844
or I guess you could say the
chromosomes are being moved

00:05:41.844 --> 00:05:43.667
and these things are
pushing each other apart.

00:05:43.667 --> 00:05:45.072
The two centrosomes might be pushing apart

00:05:45.072 --> 00:05:48.671
to get to the opposite
ends of the actual cell,

00:05:48.671 --> 00:05:50.609
but they're bringing,

00:05:50.609 --> 00:05:52.165
there's all sorts of
interesting mechanisms

00:05:52.165 --> 00:05:54.313
that are bringing along
these microtubules,

00:05:54.313 --> 00:05:56.530
bringing the chromosomes,

00:05:56.530 --> 00:05:58.794
once again splitting the homologous pairs.

00:05:58.794 --> 00:06:00.732
And how they split is random.

00:06:00.732 --> 00:06:02.926
You know, this pink one could
have been on the right side,

00:06:02.926 --> 00:06:04.087
this orange one could have
been on the left side,

00:06:04.087 --> 00:06:05.388
or vice versa, and once again,

00:06:05.388 --> 00:06:10.388
this adds more variation
amongst the gametes,

00:06:12.365 --> 00:06:15.685
so even all of the resulting
gametes that get produced,

00:06:15.685 --> 00:06:19.423
they all will have different
genetic information.

00:06:19.423 --> 00:06:20.932
So this is anaphase I.

00:06:20.932 --> 00:06:22.209
You're pulling these apart, and

00:06:22.209 --> 00:06:25.315
then you could imagine what
happens in telophase I.

00:06:25.332 --> 00:06:30.332
So telophase I, telophase, telophase I.

00:06:32.564 --> 00:06:36.553
Telophase I, and this is fairly analogous

00:06:36.553 --> 00:06:39.502
to what happens in mitosis in telophase.

00:06:39.502 --> 00:06:44.221
So now you have your
cytokinesis is beginning,

00:06:44.412 --> 00:06:47.001
and actually, it might even begin earlier,

00:06:47.001 --> 00:06:49.811
in mitosis it happens
as early as anaphase,

00:06:49.811 --> 00:06:51.540
at least the cytokinesis is starting,

00:06:51.540 --> 00:06:53.119
but you're starting to see that.

00:06:53.119 --> 00:06:58.119
The homologous pairs
are fully split apart,

00:06:58.378 --> 00:06:59.794
and they're at opposite ends,

00:06:59.794 --> 00:07:03.451
and actually they can begin to unravel

00:07:03.451 --> 00:07:04.856
into their chromatin state,

00:07:04.856 --> 00:07:09.856
so this one began to unravel
into its chromatin state.

00:07:10.359 --> 00:07:12.327
It has a little bit of the magenta.

00:07:12.390 --> 00:07:16.877
Oops, it has a little bit of
the magenta right over here.

00:07:17.278 --> 00:07:19.530
This is unravelling as well.

00:07:19.530 --> 00:07:22.177
This is unravelling like that,

00:07:22.177 --> 00:07:24.127
once it gets into its chromatin state.

00:07:24.127 --> 00:07:28.376
The cellular, and let me
do the other ones as well.

00:07:28.376 --> 00:07:32.207
So this is this one right over here.

00:07:32.207 --> 00:07:34.686
It's beginning to unravel.

00:07:35.248 --> 00:07:39.114
This one over here, beginning to unravel.

00:07:39.114 --> 00:07:41.384
It's got a bit of orange on it.

00:07:41.668 --> 00:07:42.968
It's got a little bit of orange on it.

00:07:42.968 --> 00:07:45.847
The nuclear membrane begins to form again.

00:07:45.847 --> 00:07:50.822
The nuclear membrane begins to form again.

00:07:51.791 --> 00:07:54.368
In some ways, it's reversing
what happened in prophase I

00:07:54.368 --> 00:07:55.750
where the nuclear membrane disappeared,

00:07:55.750 --> 00:07:58.159
and the chromosomes condensed.

00:07:58.524 --> 00:08:03.522
And let me draw, let me
draw the centrosomes,

00:08:03.632 --> 00:08:06.732
which are outside the nuclear
membrane, just like that.

00:08:06.732 --> 00:08:09.664
And the microtubules are also dissolving.

00:08:09.866 --> 00:08:11.747
The microtubules are also dissolving.

00:08:11.747 --> 00:08:14.591
And you have your cytokinesis.

00:08:14.591 --> 00:08:17.006
So your cytokinesis, so these separate.

00:08:17.006 --> 00:08:20.379
These separate into two cells.

00:08:20.512 --> 00:08:22.311
So once again, when we did the overview

00:08:22.311 --> 00:08:26.406
of meiosis, we said look,
the first phase of meisosis,

00:08:26.406 --> 00:08:31.406
you go from a diploid germ
cell to two haploid cells.

00:08:32.250 --> 00:08:35.283
And these aren't quite
our end product yet.

00:08:35.283 --> 00:08:37.546
This right over here, what
we have just gone through,

00:08:37.546 --> 00:08:39.323
what we have just gone through,

00:08:39.323 --> 00:08:42.608
all of this combined that
we have just gone through,

00:08:42.608 --> 00:08:44.268
this is meiosis I.

00:08:44.268 --> 00:08:48.482
And in the next video, we're
gonna go through meiosis II.

00:08:48.482 --> 00:08:50.775
Whoops, I didn't mean to do that.

00:08:51.141 --> 00:08:56.141
This is, so let's see,
all of this is meiosis I.

00:08:56.620 --> 00:08:59.610
Let me write that in a
different color, in bold.

00:09:00.103 --> 00:09:04.712
So this is all meiosis, meiosis I here,

00:09:04.712 --> 00:09:07.242
and you can see each of these cells now

00:09:07.242 --> 00:09:08.740
have a haploid number.

00:09:08.740 --> 00:09:13.186
They now have a haploid, haploid number

00:09:13.186 --> 00:09:15.183
of two chromosomes each.

00:09:15.183 --> 00:09:16.460
Now each of those two chromosomes

00:09:16.460 --> 00:09:20.418
do have two sister chromatids,

00:09:20.418 --> 00:09:22.543
and as we'll see in meiosis II,

00:09:22.543 --> 00:09:24.598
which is very similar to mitosis,

00:09:24.598 --> 00:09:27.419
is going to split up the sister chromatids

00:09:27.419 --> 00:09:28.661
from each of these chromosomes,

00:09:28.661 --> 00:09:32.120
which gives us two daughter chromosomes.

00:09:32.120 --> 00:09:33.583
So we're gonna see that over here.

00:09:33.583 --> 00:09:35.278
So your haploid number here is two.

00:09:35.278 --> 00:09:37.008
You have two chromosomes here and

00:09:37.008 --> 00:09:38.517
you have two chromosomes there.

00:09:38.517 --> 00:09:42.017
And we'll explore meiosis
II in the next video.


Chromosomal crossover in Meiosis I

WEBVTT
Kind: captions
Language: en

00:00:00.388 --> 00:00:04.083
- Let's now jump into understanding
meiosis in some depth.

00:00:04.083 --> 00:00:06.647
So let's start with the germ cell.

00:00:07.523 --> 00:00:10.541
As we mentioned already,
a germ cell is a cell that

00:00:10.541 --> 00:00:14.454
it can either go to mitosis
to produce other germ cells

00:00:14.454 --> 00:00:18.761
or it can undergo meiosis
in order to produce gametes.

00:00:18.761 --> 00:00:21.582
So this is a germ cell right over here.

00:00:21.582 --> 00:00:24.101
Let me draw the nuclear membrane.

00:00:25.371 --> 00:00:28.327
Let me draw the nucleus
larger because that's where

00:00:28.327 --> 00:00:31.306
we care a lot about the chromosomes in it.

00:00:31.306 --> 00:00:33.175
And let me draw a centrosome

00:00:33.175 --> 00:00:35.589
which will play a role later on.

00:00:35.589 --> 00:00:37.505
I wanna do that in ...

00:00:37.505 --> 00:00:39.328
Let's see, I'll do that
in this blue color.

00:00:39.328 --> 00:00:41.947
Each centromosome has
two centrioles in it.

00:00:43.647 --> 00:00:45.859
I just wanna clarify
some of the terminology.

00:00:45.859 --> 00:00:48.459
And in the mitosis videos, I focused on

00:00:49.609 --> 00:00:52.282
cells of an organism, I
just kind of made it up,

00:00:52.282 --> 00:00:56.183
that had two chromosomes, that
had a diploid number of two

00:00:56.183 --> 00:00:59.747
that had one homologous
pair, that had one chromosome

00:00:59.747 --> 00:01:01.360
from each of its parents.

00:01:01.360 --> 00:01:04.328
For this video, I'm
gonna focus on a species,

00:01:04.328 --> 00:01:06.070
not human beings, that would have

00:01:06.070 --> 00:01:08.531
23 pairs or 46 chromosomes.

00:01:08.531 --> 00:01:10.953
I'm gonna focus on a species that has,

00:01:10.953 --> 00:01:13.414
that's diploid number is four.

00:01:13.414 --> 00:01:17.733
And so, let's say it has two
chromosomes from the father.

00:01:17.733 --> 00:01:18.917
And let me do that.

00:01:18.917 --> 00:01:20.329
I'll do that in this orange color.

00:01:20.329 --> 00:01:21.273
Now, I'll do that in the chromatin,

00:01:21.273 --> 00:01:23.177
I'll kind of depict the chromatin state,

00:01:23.177 --> 00:01:24.071
it's kind of unwound.

00:01:24.071 --> 00:01:25.925
So maybe it has a long one from the father

00:01:25.925 --> 00:01:28.513
and it has a short one from the father.

00:01:28.513 --> 00:01:31.230
And then it has homologous
chromosomes from the mother.

00:01:31.230 --> 00:01:33.807
So it would have the
long one from the mother

00:01:33.807 --> 00:01:37.780
and it would have the short one

00:01:37.780 --> 00:01:39.928
from the mother just like that.

00:01:39.928 --> 00:01:42.881
And obviously this is
a huge simplification

00:01:42.881 --> 00:01:44.726
but hopefully this
discuss the point across.

00:01:44.726 --> 00:01:47.722
So here, it has a diploid
number of chromosomes.

00:01:47.722 --> 00:01:50.434
So this is, let me write this down.

00:01:50.434 --> 00:01:55.088
This is diploid

00:01:55.088 --> 00:01:57.890
number is equal to,

00:01:57.890 --> 00:02:00.026
we have four chromosomes.

00:02:00.026 --> 00:02:02.104
And then this thing, this germ cell.

00:02:02.104 --> 00:02:02.963
Let me write this down.

00:02:02.963 --> 00:02:05.470
This is a germ cell right over here.

00:02:05.470 --> 00:02:08.164
It will go through interphase.

00:02:08.164 --> 00:02:09.882
So let me draw that.

00:02:09.882 --> 00:02:13.202
So it will go through interphase, in which

00:02:13.202 --> 00:02:18.202
it grows and it can replicate
its DNA and its centrosome.

00:02:18.229 --> 00:02:19.923
And so, let me draw that.

00:02:19.923 --> 00:02:22.210
So after it goes through interface,

00:02:22.210 --> 00:02:24.962
I wanna use my space
carefully because I have a lot

00:02:24.962 --> 00:02:26.645
of steps to go through.

00:02:26.645 --> 00:02:31.428
After it goes through
interface, I am going to have

00:02:31.428 --> 00:02:35.760
in my nucleus here,

00:02:36.718 --> 00:02:38.831
my DNA will have replicated.

00:02:38.831 --> 00:02:42.848
So this long chromosome from my father,

00:02:42.848 --> 00:02:46.361
now all the DNA will have replicated so

00:02:46.361 --> 00:02:49.925
it may look something like that.

00:02:49.925 --> 00:02:54.567
And it's attached

00:02:54.567 --> 00:02:56.157
at a centromere,

00:02:56.157 --> 00:02:58.026
All these centro words,

00:02:58.026 --> 00:02:59.861
at a centromere right here.

00:02:59.861 --> 00:03:01.296
But I'm still trying to draw it in kind of

00:03:01.296 --> 00:03:02.620
the chromatin state.

00:03:02.620 --> 00:03:03.672
It's actually all spread out.

00:03:03.672 --> 00:03:06.133
It's not bunched up so that
you can see it very clearly

00:03:06.133 --> 00:03:10.173
as these X's in a simple microscope.

00:03:10.173 --> 00:03:11.399
So it's just replicated.

00:03:11.399 --> 00:03:14.499
And after replicating, it
is still one chromosome.

00:03:14.499 --> 00:03:16.589
It has twice the genetic material

00:03:16.589 --> 00:03:19.166
but it is still one chromosome.

00:03:19.166 --> 00:03:21.580
That one chromosome is now made up of

00:03:21.580 --> 00:03:24.320
two sister chromatids.

00:03:24.320 --> 00:03:27.610
we talked a lot about
that in the mitosis video,

00:03:27.610 --> 00:03:28.991
but it doesn't hurt to reinforce

00:03:28.991 --> 00:03:30.872
because it can get a little bit confusing.

00:03:30.872 --> 00:03:34.888
And then you have that shorter
chromosome from the father

00:03:34.888 --> 00:03:39.888
and then that also replicates
into two sister chromatids

00:03:40.008 --> 00:03:43.050
attached at a centromere.

00:03:43.050 --> 00:03:45.847
So these are still two
chromosomes from the father.

00:03:45.847 --> 00:03:48.819
It has twice the amount
of DNA but it's containing

00:03:48.819 --> 00:03:49.887
the same information,

00:03:49.887 --> 00:03:52.139
just duplicate versions
of that same information.

00:03:52.139 --> 00:03:54.728
And the same thing's gonna
happen from the mother.

00:03:54.728 --> 00:03:57.259
You had that long
chromosome from the mother,

00:03:57.259 --> 00:03:59.244
homologous to this right over here.

00:03:59.244 --> 00:04:01.427
It's going to replicate.

00:04:01.427 --> 00:04:06.384
So it's now going to be
two sister chromatids.

00:04:06.384 --> 00:04:08.647
And then you have a short
strand from the mother

00:04:08.647 --> 00:04:11.027
that was homologous to
this one from your father.

00:04:11.027 --> 00:04:13.140
And that's also gonna replicate.

00:04:13.140 --> 00:04:14.638
And so, it's like that.

00:04:14.638 --> 00:04:15.926
And at the end of interface,

00:04:15.926 --> 00:04:18.387
it would actually all be spread out.

00:04:18.387 --> 00:04:20.384
Once again, it won't be
bunched up into these

00:04:20.384 --> 00:04:22.183
clearly discernible X's.

00:04:22.183 --> 00:04:23.797
I drew them a little
bit that way, otherwise,

00:04:23.797 --> 00:04:26.281
because you would have trouble
seeing how that replicated.

00:04:26.281 --> 00:04:30.871
And we also have replicated our centrosome

00:04:30.871 --> 00:04:33.112
as we've gone through interphase.

00:04:33.112 --> 00:04:34.679
Now, we are ready.

00:04:34.679 --> 00:04:38.591
In fact, now we are ready for
either mitosis or meiosis.

00:04:38.591 --> 00:04:40.391
But as I said, the focus of this video

00:04:40.391 --> 00:04:44.943
is going to be meiosis
so let's do some meiosis.

00:04:45.657 --> 00:04:46.709
So the first phase,

00:04:46.709 --> 00:04:49.888
so the first several
phases we call meiosis I.

00:04:49.888 --> 00:04:52.700
And the beginning of
meiosis I is prophase I.

00:04:52.700 --> 00:04:55.207
So let's see what happens in prophase I.

00:04:55.207 --> 00:04:56.771
So prophase I.

00:04:57.717 --> 00:05:00.967
And so, let me draw the
cell right over here.

00:05:02.074 --> 00:05:04.907
So prophase I.

00:05:04.907 --> 00:05:06.625
A couple of things happen.

00:05:06.625 --> 00:05:09.005
The nuclear membrane begins to dissolve.

00:05:09.005 --> 00:05:12.831
This is very similar to prophase

00:05:12.831 --> 00:05:15.701
when we're looking at mitosis.

00:05:15.701 --> 00:05:19.462
So the nuclear envelope
begins to dissolve.

00:05:19.462 --> 00:05:22.783
These things start to
maybe migrate a little bit.

00:05:22.783 --> 00:05:27.705
So these characters are trying
to go at different ends.

00:05:27.705 --> 00:05:31.187
And the DNA starts to
bunch up into kind of

00:05:31.187 --> 00:05:32.883
its condensed form.

00:05:32.883 --> 00:05:34.565
So now I can draw it.

00:05:34.565 --> 00:05:37.340
So now I can start to draw it as proper.

00:05:37.340 --> 00:05:40.805
So this is the one from the father

00:05:42.076 --> 00:05:43.596
right over here.

00:05:43.596 --> 00:05:46.452
And this is the one from the mother.

00:05:46.452 --> 00:05:48.716
And I'm drawing, I'm
overlapping on purpose

00:05:48.716 --> 00:05:50.434
because something very interesting happens

00:05:50.434 --> 00:05:52.490
especially in meiosis.

00:05:52.490 --> 00:05:55.750
So it's the mother right over here.

00:05:57.360 --> 00:05:58.014
Let me see.

00:05:58.014 --> 00:05:59.675
Let's now do the centromere in blue now.

00:05:59.675 --> 00:06:02.973
That's the centromere.

00:06:02.973 --> 00:06:06.734
Now this is the shorter
ones from the father.

00:06:07.832 --> 00:06:10.907
These are the shorter
ones from the mother.

00:06:10.907 --> 00:06:12.800
And actually, let me just do
draw them on opposite sides

00:06:12.800 --> 00:06:14.100
just to show that they don't have to,

00:06:14.100 --> 00:06:15.091
the ones from the father aren't always

00:06:15.091 --> 00:06:16.716
on the left hand side.

00:06:16.716 --> 00:06:20.072
So this is the shorter
one from the father.

00:06:20.072 --> 00:06:21.479
They couldn't be all on the left hand side

00:06:21.479 --> 00:06:23.096
but doesn't this all they have to be.

00:06:23.096 --> 00:06:24.734
And this is the shorter
one from the mother.

00:06:24.734 --> 00:06:27.391
And I will draw this overlapping
although they could have.

00:06:27.391 --> 00:06:29.446
Shorter one from the mother.

00:06:29.446 --> 00:06:31.814
And once again, each of these,
this is a homologous pair,

00:06:31.814 --> 00:06:33.975
that's a homologous pair over there.

00:06:33.975 --> 00:06:37.028
Now, the DNA has been replicated so

00:06:37.028 --> 00:06:40.255
in each of the chromosomes
in a homologous pair,

00:06:40.255 --> 00:06:42.415
you have two sister chromatids.

00:06:42.415 --> 00:06:44.886
And so, in this entire homologous pair,

00:06:44.886 --> 00:06:47.569
you have four chromatids.

00:06:47.569 --> 00:06:49.948
And so, this is sometimes called a tetrad.

00:06:49.948 --> 00:06:53.165
So let me just give
ourselves some terminology.

00:06:53.165 --> 00:06:56.426
So this right over here is called a tetrad

00:06:56.426 --> 00:06:59.351
or often called a tetrad.

00:06:59.351 --> 00:07:01.348
Now, the reason why I
drew this overlapping

00:07:01.348 --> 00:07:04.435
is when we are in prophase I in meiosis I.

00:07:04.435 --> 00:07:05.573
Let me label this.

00:07:05.573 --> 00:07:09.172
This is prophase I.

00:07:09.172 --> 00:07:11.772
You can get some genetic recombination,

00:07:11.772 --> 00:07:13.455
some homologous recombination.

00:07:13.455 --> 00:07:16.163
Once again, this is homologous pair.

00:07:16.163 --> 00:07:18.265
One chromosome from the father

00:07:18.265 --> 00:07:19.611
that I've gotten from the father.

00:07:19.611 --> 00:07:22.389
The species or the cell got
it from its father's cell

00:07:22.389 --> 00:07:24.780
and one from the mother.

00:07:24.780 --> 00:07:26.219
And they're homologous.

00:07:26.219 --> 00:07:28.123
They might contain different base pairs,

00:07:28.123 --> 00:07:33.123
different actual DNA, but
they code for the same genes.

00:07:34.355 --> 00:07:38.022
Over simplification, but in a
similar place on each of these

00:07:38.022 --> 00:07:41.609
it might code for eye
color or I don't know,

00:07:41.609 --> 00:07:42.839
personality.

00:07:42.839 --> 00:07:45.300
Nothing is that simple in how tall you get

00:07:45.300 --> 00:07:48.690
and it's not that simple
in DNA but just to give you

00:07:48.690 --> 00:07:49.909
an idea of how it is.

00:07:49.909 --> 00:07:51.755
And the reason why I
overlapped them like this

00:07:51.755 --> 00:07:54.831
is to show how the
recombination can occur.

00:07:54.831 --> 00:07:56.108
So actually, let me zoom in.

00:07:56.108 --> 00:07:59.011
So this is the one from the father.

00:07:59.011 --> 00:08:00.856
Once again, it's on the condensed form.

00:08:00.856 --> 00:08:05.012
This is one chromosome made
up of two sister chromatids

00:08:05.012 --> 00:08:06.289
right over here.

00:08:06.289 --> 00:08:08.054
And I drew the centromere,

00:08:08.054 --> 00:08:10.051
not to be confused with centrosomes.

00:08:10.051 --> 00:08:13.348
That's where they are, those
sister chromatids are attached.

00:08:13.348 --> 00:08:17.690
And then, I will draw the homologous

00:08:17.690 --> 00:08:19.895
chromosome from the mother.

00:08:19.895 --> 00:08:23.030
So the homologous
chromosome from the mother

00:08:23.030 --> 00:08:27.232
just like that.

00:08:28.052 --> 00:08:30.718
Homologous chromosome from the mother.

00:08:30.718 --> 00:08:33.876
And the recombination can occur at a point

00:08:33.876 --> 00:08:35.606
right over here.

00:08:35.606 --> 00:08:38.996
So after you're done
with the recombination,

00:08:38.996 --> 00:08:41.677
this side might look
something more like this.

00:08:41.677 --> 00:08:46.308
So let me draw it like this.

00:08:46.308 --> 00:08:48.456
So, they essentially break up

00:08:48.456 --> 00:08:50.639
and they swap those little sections.

00:08:50.639 --> 00:08:52.113
There's one way to think about it.

00:08:52.113 --> 00:08:56.340
So this one, we'll now have a
little piece from the mother.

00:08:56.340 --> 00:08:58.150
It might code for similar genes.

00:08:58.150 --> 00:09:00.576
But now it contains the
mother's genetic information.

00:09:00.576 --> 00:09:03.697
And then this one over here

00:09:06.384 --> 00:09:10.962
will now have the piece.

00:09:10.962 --> 00:09:14.548
And you could say even
homologous piece from the father.

00:09:16.190 --> 00:09:18.860
Let me do these two centromeres.

00:09:18.860 --> 00:09:20.032
And this is really interesting.

00:09:21.242 --> 00:09:23.437
All the time, there
couldn't be recombination

00:09:23.437 --> 00:09:26.897
and often times it can lead to
kind of non-optimal things,

00:09:26.897 --> 00:09:28.731
nonsense code and DNA.

00:09:28.731 --> 00:09:31.796
It might lead to a nonfunctional organism.

00:09:31.796 --> 00:09:36.149
But this happens fairly
common in the meiosis

00:09:36.149 --> 00:09:38.751
and it's a way, once again,
to get more variation.

00:09:38.751 --> 00:09:40.549
We've talked about sexual
reproduction before.

00:09:40.549 --> 00:09:43.370
And sexual reproduction
introduces variation

00:09:43.370 --> 00:09:44.868
into a population.

00:09:44.868 --> 00:09:46.934
And this, obviously, when different sperms

00:09:46.934 --> 00:09:48.954
find different eggs that
introduces variation.

00:09:48.954 --> 00:09:50.649
But then, even amongst homologous pairs

00:09:50.649 --> 00:09:54.666
you can actually have exchange
between this chromosome.

00:09:54.666 --> 00:09:57.255
And that's interesting
because as we mentioned,

00:09:57.255 --> 00:09:58.253
each of these chromosomes,

00:09:58.253 --> 00:10:00.830
they code for a bunch of different genes.

00:10:00.830 --> 00:10:03.024
And a gene is kinda
looking code for a specific

00:10:03.024 --> 00:10:05.891
or a set of proteins.

00:10:05.891 --> 00:10:08.306
So this right over here,

00:10:09.246 --> 00:10:11.053
and this is what I'm about
to say is gonna be huge

00:10:11.053 --> 00:10:12.364
over simplification.

00:10:12.364 --> 00:10:15.627
Maybe right over here
you coded for eye color

00:10:15.627 --> 00:10:18.308
or it was related to, or it
helps code for eye color.

00:10:18.308 --> 00:10:19.946
And then you got that from your dad.

00:10:19.946 --> 00:10:21.710
And here, it helped code for eye color.

00:10:21.710 --> 00:10:22.789
And you got that from your mom.

00:10:22.789 --> 00:10:26.191
Your mom might have trended
you towards a lighter eye color

00:10:26.191 --> 00:10:27.549
and your dad might have trended you

00:10:27.549 --> 00:10:28.907
towards a darker eye color.

00:10:28.907 --> 00:10:32.030
But now, the one from your
mom is on this chromosome,

00:10:32.030 --> 00:10:34.279
this gene, and then the one

00:10:34.279 --> 00:10:35.557
or they've both the same gene.

00:10:35.557 --> 00:10:36.717
They're just different allele.

00:10:36.717 --> 00:10:38.831
They're coding for different
variance of that gene.

00:10:38.831 --> 00:10:41.291
And then the allele from
your dad is over here.

00:10:41.291 --> 00:10:44.298
And once again, some people
get confused with genes

00:10:44.298 --> 00:10:45.612
and chromosomes and all of these.

00:10:45.612 --> 00:10:48.519
Each of these chromosomes
contain a bunch of genes.

00:10:48.519 --> 00:10:50.979
These are very long DNA molecules.

00:10:50.979 --> 00:10:53.626
This code for a bunch of different genes.

00:10:53.626 --> 00:10:57.434
So gene will be a little section
of here that could code for

00:10:57.434 --> 00:10:59.408
a particular protein.

00:10:59.408 --> 00:11:01.590
So that's what happens in prophase I.

00:11:01.590 --> 00:11:05.034
In prophase I, you have this condensation

00:11:05.034 --> 00:11:09.732
of your chromosomes, of
your homologous pairs.

00:11:09.732 --> 00:11:12.646
You can have this recombination.

00:11:12.646 --> 00:11:14.365
And it's really interesting,
this recombination

00:11:14.365 --> 00:11:16.120
doesn't tend to happen
at just random points

00:11:16.120 --> 00:11:20.149
that would kind of break
the genetic information.

00:11:20.149 --> 00:11:22.667
It tends to happen at fairly clean points.

00:11:22.667 --> 00:11:25.344
And the places where this
breakup is happening,

00:11:25.344 --> 00:11:27.515
these are called the plural,

00:11:27.515 --> 00:11:30.057
if you just talk about
one point, it's a chiasma,

00:11:30.057 --> 00:11:32.797
or if you're talking about
the plural, it's chiasmata.

00:11:32.797 --> 00:11:34.597
Sounds like it could be a horror movie.

00:11:34.597 --> 00:11:36.698
So, chiasma.

00:11:36.698 --> 00:11:37.835
Chiasma.

00:11:37.835 --> 00:11:38.996
And the fact that they happen,

00:11:38.996 --> 00:11:41.295
they tend to happen fairly
cleanly, this is once again,

00:11:41.295 --> 00:11:43.713
kind of the beauty of
the universe or at least

00:11:43.713 --> 00:11:46.197
of biology is that through

00:11:46.197 --> 00:11:50.760
billions of years of evolution,
these things have kind of

00:11:50.760 --> 00:11:54.370
optimized for more variation and to happen

00:11:54.370 --> 00:11:56.239
in fairly clean ways.

00:11:56.239 --> 00:11:58.146
So I'm gonna leave this video right there.

00:11:58.146 --> 00:11:59.307
I know I just got to prophase I.

00:11:59.307 --> 00:12:01.907
But this was a really,
really important idea of

00:12:01.907 --> 00:12:06.272
this homologous recombination
or this chromosomal crossover

00:12:06.272 --> 00:12:07.828
that we see right over here.

00:12:07.828 --> 00:12:09.364
And then from there, we can continue

00:12:09.364 --> 00:12:13.410
through the rest of meiosis
I and then meiosis II.