11.4 Warm Up

1.      What are the steps in oogenesisi?

         Primordial germ cell divide by mitosis to produce two Oogonia. These cells are all Diploid.

·         Each Oogonia also undergoes mitosis to produce two diploid Primary Oocytes

·         Each Oocyte starts to undergo meiosis I replicating their DNA, but stops in at prophase I

·         There are approx 400,000 primary follicles present in the ovary prior to puberty.

·         A Primary follicles (prophase I) may develop to secondary follicles (metaphase II) under the influence of FSH.

·         Note that the first polar body ( haploid set chromosomes) does not progress beyond metaphase II.

·         The Oocyte does not progress to the end of meiosis unless fertilisation takes place.

1.      What are the steps in spermatogenesis?

Spermatogonium (2n) are found at or near the basement membrane. Cell division by mitosis to produce spermatogonia. The spermatogonium grow to form Primary Spermatocytes which have completed S-phase. The Primary spermatocytes separate the homologous pairs of chromosomes in meiosis I to form the haploid Secondary Spermatocytes. The spermatids are formed from the separation of the sister chromatids in meiosis II. The spermatids are found in association with the sertoli cells which nourish the spermatids as they differentiate into spermatozoa. The rate of spermatozoa is high and continuous throughout the life on the sexually mature male. The average number of spermatozoa in ejaculated semen is 32 x 10⁶ ml^-1

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