Gametogenesis is the process of forming gametes with a haploid number of chromosomes (n) from diploid cells (2n) of the germ line
In animals and humans, male gametogenesis is referred to as spermatogenesis that takes place in the gonads, the testes. In humans sperm production begins at puberty at continues throughout life. In the testicles spermatogonia are produced through mitosis that then undergo meiosis producing four sperm each. After meiosis the products of meiosis differentiate into functional sperm. Several hundred million (200 000 000) sperm are produced each day. Once sperm form they move into the epididymis, where they mature and are stored.
This figure demonstrates spermatogenesis with two chromosome pairs.
In females oogenesis is the process of forming ova (eggs) through meiosis in the gonads known as ovaries. An ovary contains many follicles composed of developing eggs surrounded by an outer layer of follicle cells. Diploid stem cells called oogonia divide by mitosis to produce more oogonia and primary oocytes. Each egg begins oogenesis as a primary oocyte. At birth each female carries a lifetime supply of developing oocytes, a total of 400-500 eggs, each of which is in prophase I. A developing egg (secondary oocytes) is released each month from puberty until menopause. Secondary oocytes only complete meiosis once it is fertilized. In contrast to spermatogenesis where all four products of meiosis develop into gametes, only one of the four products of oogenesis becomes an egg. Most of the cytoplasm is placed in one cell, the egg, the other three do not develop and are much smaller than the egg and are called polar bodies.
This figure demonstrates oogenesis with two chromosome pairs.