GAMETOGENESIS

Prof. Preety SinhaDeptt. Of Zoology

A. N. College, Patna

INTRODUCTION

• Gametogenesis is the process whereby a haploidcell (n) is formed from a diploid cell (2n) throughmeiosis and cell differentiation.

• Gametogenesis in the male is knownas 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 tubulesof the testes (male gonads).I

Inside the wall of the seminiferous tubules diploid stem cells are present calledspermatogonium.

When Leydig cells release testosterone, this hormone goes on to stimulatespermatogonium to differentiate into the primary spermatocyte

The primary spermatocyte can then undergo meiosis I to produce two haploidcells called secondary spermatocytes.

SPERMATOGENESIS

Each of these secondary spermatocytes then undergoes meiosis II toproduce a total of four spermatids.

With the help of Sertoli cells, the haploid spermatids then differentiateinto sperm cells.

Sertoli cells function to produce nutrients to the developing sperm cellsas well as remove the cytoplasm.

Once the sperm cells are differentiated, they swim up to theepididymis, 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 toincrease in number, eventually resulting in up to one to two million cells inthe 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 prophasestage.

Anterior pituitary hormones cause the development of a number of folliclesin 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 organellesgoing to one cell, called a secondary oocyte, and only one set of chromosomesand a small amount of cytoplasm going to the other cell called polar body whichusually die.

A secondary meiotic arrest occurs, this time at the metaphase II stage. Atovulation, this secondary oocyte will be released and travel toward the uterusthrough 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 eggcontaining all 46 chromosomes of a human being, half of them coming from thesperm.

TTHANK YOU