True statement regarding oogenesis is/are:a) Primary occyte arrests in prophase of 1st meiotic divisionb) Primary occyte arrests in prophase of 2nd meiotic divisionc) Secondary oocyte arrest in Metaphase of 1st meiotic divisiond) Secondary oocyte arrest in Metaphase of 2nd meiotic divisione) 1st polar body is extruded during 1st meiotic division of primary oocytes
The process involved in the development of mature ovum is called Oogenesis.
The primitive germ cells take their origin from yolk sac at about the end of 3rd week and migrate to the developing gonadal ridge, at about the end of 4th week.
Important facts:

Oogenesis begins in the ovary at 6-8 weeks of gestation.
Maximum number of oocytes/oogonia are in the ovary at 5th month of development (20 weeks of gestation number being 6-7 million).
At birth no more mitotic division occur, all oogonia are replaced by primary oocyte.
At birth total content of both ovaries is 2 million primary oocytes.
At puberty number is further decreased and is ~ 300000-500000, of which only 500 are destined to mature during an individual’s life time.
All the primary oocytes in the ovary of a newborn are arrested in the diplotene stage of prophase (of meiosis).
All the primary oocytes then remain arrested and the arrested phase is called as “Dictyate stage” till puberty.
The primary oocyte gets surrounded by follicular cells in the ovary and this structure is now called as Primordial follicle.
At puberty as a result of mid cycle preovulatory surge, meiosis is resumed and completed just prior to ovulation.
Therefore first polar body is released just prior to ovulation or along with ovulation..
The second division starts immediately after it and is arrested in metaphase.
At the time of fertilization second division is completed which results in the release of oocyte and second polar body.
Therefore second polar body is released only at the time of fertilisation.
Size of mature ovum = 120-130 μm (It is the largest cell in the body).
Size of mature follicle = 18-20 mm
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