AP BIOLOGY

Detailed explanation-1: -In oogenesis, diploid oogonium go through mitosis until one develops into a primary oocyte, which will begin the first meiotic division, but then arrest; it will finish this division as it develops in the follicle, giving rise to a haploid secondary oocyte and a smaller polar body.

Detailed explanation-2: -The primary oocyte is a diploid cell & is formed from the oogonia/gamete mother cell by mitotic division. It gives rise to secondary oocytes after the meiosis-I division. These secondary oocytes are haploid.

Detailed explanation-3: -The oogonia proliferate by mitotic division, become invested with a single layer of granulosa cells, and differentiate into primary oocytes, the female progenitor cells.

Detailed explanation-4: -The secondary oocyte remains paused in meiosis II until a sperm cell fertilizes it. This triggers the egg to complete meiosis II. During meiosis II, the duplicated chromosomes are separated into a polar body and a mature ovum. At this point, the haploid nuclei of the egg and sperm are able to fuse to form the zygote.

Detailed explanation-5: -Just before ovulation, the oocyte rapidly completes meiosis I, dividing in such a way that one cell becomes the secondary oocyte (an egg orovum), containing most of the cytoplasm with its organelles; the other cell becomes the first polar body (seeFig. 2-17).