Gametogenesis (part – 1)

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It is the process of gamete formation in sexually reproducing organism. Sexually reproducing organism has two types of cell somatic cell and germinal cell. Both have diploid number of chromosomes. Somatic cell forms various body organs and always multiplies by mitotic division. Germinal cell form gamete in animal body by successive mitotic and meiotic division.

Process of gametogenesis is of two types: spermatogenesis and oogenesis     

Spermatogenesis

It is the formation of haploid microscopic and functional male gametes called spermatozoa from diploid reproductive cell spermatogonia (2n) that present in the testis of male body.

Process of spermatogenesis is divided into two parts:

  1. Formation of spermatid

It is further divided into three processes.

Multiplicative phase: it involve the rapid mitotic division of diploid primary germ cells that called gonocytes present in germinal epithelium of the seminiferous tubules of testis this form large number of sperm mother cells that are called spermatogonia. Some spermatogonia act as stem cells, while some other spermatogonia enter the growth phase.    

Growth phase: in this spermatogonium first increase in size by accumulation of nutritive material and called primary spermatocyte.

Maturation phase: in this diploid primary spermatocyte undergoes meiosis 1 and forms two haploid cells called secondary spermatocyte each have 23 chromosome immediately followed by meiosis 2 in each secondary spermatocyte to form two haploid spermatids each have 23 chromosome in it. Each spermatogonium produces 4 haploid spermatids.

  1. Spermiogenesis

The transformation of non-motile, rounded and haploid spermatids into functional and motile spermatozoa is called Spermiogenesis. It involve following changes:


·       Nucleus becomes condensed, narrow and anteriorly pointed due to loss of material like RNA and most of proteins.
·       Mature spermatozoa are released into lumen of seminiferous tubules. Two testis of young adult form about 120 million sperm each day.
·       Process of spermatogenesis start at the stage of puberty due to increase secretion of gonadotropin releasing hormone (GnRH) form hypothalamus of brain. GnRH stimulates the adinohypophysis to secrete two gonadotropin FSH and ICSH. FSH stimulate sertoli cell of testis to secrete certain factors that help in spermatogenesis. ICSH stimulate leydig cells of testis to secrete male sex hormone testosterone.
·       A part of Golgi body of spermatids forms the acrosome.
·       Centrioles of spermatids form the neck of sperm.
·       Mitochondria form a spiral ring behind the neck around distal Centrioles.

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