GAMETOGENESIS

Prof. Preety Sinha Deptt. Of Zoology A. N. College, Patna INTRODUCTION

• Gametogenesis is the process whereby a haploid cell (n) is formed from a diploid cell (2n) through meiosis and cell differentiation.

• Gametogenesis in the male is known as spermatogenesis and produces spermatozoa.

• Gametogenesis in the female is known as oogenesis and result in the formation of ova. SPERMATOGENESIS

 It is the process by which sperm cells are produced in the seminiferous tubules of the testes (male gonads).I  Inside the wall of the seminiferous tubules diploid stem cells are present called spermatogonium.  When Leydig cells release testosterone, this hormone goes on to stimulate spermatogonium to differentiate into the primary spermatocyte  The primary spermatocyte can then undergo meiosis I to produce two haploid cells called secondary spermatocytes. SPERMATOGENESIS

 Each of these secondary spermatocytes then undergoes meiosis II to produce a total of four spermatids.  With the help of Sertoli cells, the haploid spermatids then differentiate into sperm cells.  Sertoli cells function to produce nutrients to the developing sperm cells as well as remove the cytoplasm.  Once the sperm cells are differentiated, they swim up to the epididymis, where they mature and are stored until their release.

OOGENESIS

• Oogenesis occurs in the outermost layers of the ovaries with a germ cell, called an oogonium (plural: oogonia), but this cell undergoes mitosis to increase in number, eventually resulting in up to one to two million cells in the embryo.  The cell starting meiosis is called a primary oocyte.  This cell begin the first meiotic division but be arrested in its progress in the first prophase stage. At the time of birth, all future eggs are in the prophase stage.  Anterior pituitary hormones cause the development of a number of follicles in an ovary.  This results in the primary oocyte finishing the first meiotic division. OOGENESIS

 The cell divides unequally, with most of the cellular material and organelles going to one cell, called a secondary oocyte, and only one set of chromosomes and a small amount of cytoplasm going to the other cell called polar body which usually die.  A secondary meiotic arrest occurs, this time at the metaphase II stage. At ovulation, this secondary oocyte will be released and travel toward the uterus through the oviduct.  If the secondary oocyte is fertilized, the cell continues through the meiosis II, completing meiosis, producing a second polar body and a fertilized egg containing all 46 chromosomes of a human being, half of them coming from the sperm.

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