GAMETOGENESIS

 It is the process of formation of gametes i.e. sperm and ovum in the gonads  i.e. testis and ovary .It involves two process .

1- SPERMATOGENESIS

2- OOGENSIS 

1- SPERMATOGENESIS

Spermatogenesis is the process of formation of sperm in the testis of male 

It involves two process

A - Spermatogenesis

B- Spermiogenesis 

A - Spermatogenesis

It is the formation of spermatids from primordial germ cells.

It is divided into three phase .

a- Multiplication phase 

b-Growth phase

c- Maturation phase

a-Multiplication phase 

It is the phase , primordial  germ cells divided repidly but mitotically to produce a large number of spermatogonia having diploid number of chromosome 

b-Growth phase 

During this phase the size of nucleus as well as spermatogonial cell enlarge .

This enlargement in the size of the cells due to absorption of nutritive material form adjoining cells and also due to synthetic activity of nuclei ,acid and proteins .

These enlarged cells are now called the primary spermatocyte again having diploid number of chromosome .

During this phase splitting of chromosomes . Linkage and crossing over also take place .

c- Maturation phase 

During this phase , the primary spermatocyte under go two successive reductional cell division .

First of fall it under go miosis -1 to form two equal but haploid cells called secondary spermatocytes.

These secondary spermatocytes undergo miosis-2 to form spermatids having haploid no of chromosomes .

 B- Spermiogenesis 

It is the formation of spermatozoa from spermatids .

This process involves the formation of head , neck , middle piece and  tail .