0_Apprentice
Do you happen to know any twins?
1_Wizard
I have some friends who are fraternal twins - one a boy and one a girl
0_Apprentice
What is the difference between fraternal and identical?
1_Wizard
Identical twins develop from one zygote, while fraternal develop from two different eggs
0_Apprentice
So I guess then boy/girl twins are always fraternal.
1_Wizard
That would be correct.  Each egg has its own sperm cell
0_Apprentice
It's very interesting how twins seem to run in certain families - is it hereditary?
1_Wizard
It seems to be - the yoruba people have the highest rate of twins in the world - 90 to 100 twins per 1000 live births