a how many chromosomes are present in the developing oocytes

Solution

Ans. 1. The number of chromosomes in the developing oocyte of a baby girl = 4n

                        = 4 x (23) = 92

Ans. 2. Yes, crossing over has occurred in the developing oocyte. Only after completing recombination in pachytene, the oocyte proceeds in diplotene and remains arrested until onset of puberty.

The primordial germ cells (2n) in ovarian germinal epithelium divide mitotically to produce numerous oogonium (2n)- the cell that produces oocytes through meiosis. The oogonium (2n) duplicates its chromosome in S-phase (synthesis phase), and proceeds further into meiosis I. The resultant cell, called the primary oocyte (4n, DNA has been duplicated during S-phase, so 2n becomes 4n) remains arrested at diplotene stage of Prophase I of meiosis I until onset of puberty.