With the help of diagrammatic representation, explain the process of gametogenesis
The process of formation of gametes in sexually reproducing animals is called gametogenesis.
The germinal cells form the gametes by mitosis and meiosis.
The process of formation of male gamete or spermatozoa is called spermatogenesis.
The process of formation of female gamete or ovum is called oogenesis.
The process of spermatogenesis occurs in the seminiferous tubules of the testes of males.
Spermatogenesis includes the formation of spermatids and spermatozoa.
It involves the following phases:-
Multiplication phase: The undifferentiated primordial germ cells divide several times by mitosis to produce a large number of spermatogonia (2n).
Growth phase: Each type B spermatogonia actively grows to form a larger primary spermatocyte by obtaining nourishment from nursing cells.
Maturation phase:- Each primary spermatocyte undergoes two successive divisions called maturation divisions. The first division is reductional or meiotic division where each primary spermatocyte divides into two haploid daughter cells called secondary spermatocytes. Both secondary spermatocytes undergo a second maturation division to form four haploid spermatids from a single primary spermatocyte.
The process of oogenesis occurs in the ovaries of females.
Multiplication phase: During foetal development, certain cells of the germinal epithelium divide by mitosis and form undifferentiated germ cells called oogonia or egg mother cells (2n).
Growth phase: The oogonium grows into large primary oocytes.
Maturation phase: Each primary oocyte undergoes two maturation meiotic divisions. In the first meiotic division, the primary oocyte divides into two very unequal haploid daughter cells—a large secondary oocyte and a small first polar body or polocyte. In the second maturation division, the first polar body may divide to form two second polar bodies. The secondary oocyte again divides into unequal daughter cells—a large ootid and a very small second polar body. The ootid grows into a functional haploid ovum. One oogonium gives rise to one ovum and three polar bodies.