What is gametogenisis?

The process of formation of gametes is called “gametogenesis”. The gametes are derived from primordial germ cells/ primitive sex cells.

 • Primordial germ cells (PGC)/Primitive sex cells:Gametes are derived from PGC during 4th week of development. The PGC appear in the wall of yolk sac from which they migrate to the developing gonad from the coelomic epithelium and adjacent mesenchyme. The PGC undergo mitotic division during their migration resulting in increase in their number.

 • Definition: Gametogenesis can be defined as the process of conversion of primordial or primitive germ cells and their maturation into male and female gametes. In males it is called spermatogenesis and it takes place in seminiferous tubules of testis. In females it is called oogenesis and it takes place in the cortex of ovary.

 • Different events in gametogenesis: The process of gametogenesis includes:

1. Formation and migration of PGC and their differentiation into male or female sex cells

2. Mitotic divisions of germ cells

3. Meiotic reduction in DNA or chromosome content of the germ cells

 4. Differentiation and maturation of germ cells. Phase 1 and 2 are similar in both sexes whereas the timing and pattern of phase 3 and 4 differ.

 • The PGC are formed in the ectoderm/epiblast of the bilaminar germ disc of human embryo during 2nd week of development. They move to the wall of yolk sac by 4th week . By 5th week they reach the developing gonad.

 • Gonadal differentiation occurs in 6th week.

• The PGC undergo repeated mitotic divisions during their journey. The decision to develop into male sex cells (spermatogonia) and development of testis or female sex cells (oogonia) and ovary development depend on their own sex-chromosome constitution and on the sex determining region of Y (SRY) gene on the Y chromosome. 
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