OOGENESIS AND THE HISTOLOGY OF THE FEMALE REPRODUCTIVE SYSTEM

Question 1

Gametogenesis can be divide which four phases? [4]

Answer 1

Gametogenesis can be divide which four phases? [4]

The extraembryonic origin of germ cells and their migration to gonads

Increase in germ cell number by mitosis

Reduction in chromosome number by meiosis

Structural and functional maturation into eggs and sperm

Question 2

explain what happens during week 3 and week 6 & week 7 of origin and migration of gametogenesis?

Answer 2

week 3:

• *- primordial germ cells (pgc)** leave the primary ectoderm (epiblast) and move to the yolk sac wall and collect near the exit of the allantois
• they are now extra-embryonal, lying in the endoderm and mesoderm of the yolk sac wall

week 6:
- PGC leave the yolk sac wall and migrate along the vitelline and the dorsal mesentery into the gonadal ridge

week 7:
testosterone is formed which introduces male gonadal development (

Question 3

explain what happens during phase 2 of gametogenesis xx

Answer 3

Phase II: Increase in germ cell number

At gonads: PGC undergo rapid mitotic division. Each germ cell produces two diploid cells (2n). PGC number multiplies exponentially from hundreds to many millions. Male and female proliferation pattern is very different

Oogonia undergo intensive mitosis in embryonic ovary from the 3nd to 5^th month of maternal pregnancy. After 5 months, large numbers undergo degeneration which continues all the way through to the menopause

Question 4

explain what happens in phase 3 of gametogenesis (Phase III: Reduction in chromosome number (Meiosis))

Answer 4

Meiosis involves 2 cell divisions and 4 main events.

Cell divisions:

1. Meiosis I (reduction division) – diploid (2n) to haploid (1n). The diploid number (2n) is restored on fusion of two gametes.
2. Meiosis II (equatorial division)- independent re- assortment of maternal and paternal chromosomes.

4 main events of this include:

1. DNA replication but still 2n and 2c.
2. Pairing of homologous chromosomes and crossing over occurs during prophase. The complex of the homologous chromosome pair consisting of four chromatids is a tetrad. The result of crossing over is that there are now four recombinant chromatids. Cells now 2n and 4c.
3. Separation of chromosomes as a result of the first meiotic division. The two resulting daughter cells each have one of a pair of replicated chromosomes. Cells now 1n and 2c.
4. Separation of chromatids occurs as a result of the second meiotic division. The resulting four daughter cells each contain a haploid set of chromosomes (1n) and one chromatid (1c).

Question 5

meiosis in females: