Ans. Spermatogenesis
Some cells present 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-l and produces two haploid daughter cells called secondary spermatocytes. These cells undergo meiosis-II. In this way four haploid spermatids are produced from each primary spermatocyte.
The spermatids are non-motile and many changes occur in them to convert them into motile cells. Their nuclei shrink and some structures are formed e.g. a corner called acrosome, a tail and a mitochondria! 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 oogpnia produce diploid primary oocytes. One of the primary oocytes completes meiosis-l and produces two haploid cells.
The smaller cell is called first polar body and the larger one is called secondary oocytes.
The secondary oocytes completes meiosis-l I and produce two haploid cells i.e. a second polar body and an egg cell. Figure 14.17