Q11. What is gametogenesis? Explain the spermatogenesis and oogenesis in detail.
Definition
The formation of gametes is called gametogenesis.
Explanation
During gametogenesis, diploid (2N) gamete mother cells undergo meiosis and form haploid (1N) gametes. The male and female gametes are formed in specialized organs called gonads.
Male Gonads
Male gonads are called testes and the production of sperms in testes is called spermatogenesis.
Female Gonads
Female gonads are called ovaries and the production of egg cells in ovaries is called oogenesis.
Spermatogenesis
Some cells in the walls of the seminiferous tubules of testes divide repeatedly by mitosis to form large number of diploid spermatogonia. Some spermatogonia produce primary spermatocytes. Each primary spermatocyte undergoes meiosis-I and produces two haploid daughter cells called secondary spermatocytes. By meiosis-II, they produce four haploid spermatids. Their nuclei shrink and some structures are formed e.g. a corner called acrosome, a tail and a mitochondrial ring. After these changes, the spermatids are called sperms.
Oogenesis.
Some cells of ovary prepare structures called follicles in which many diploid oogonia are present. Some oogonia produce diploid primary oocytes. One of the primary oocyte produces two haploid cells by meiosis. The smaller cell is called first polar body and the large one is called secondary oocytes. The secondary oocyte completes meiosis II and produces two haploid cells i.e. a second polar body and an egg cell.