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Gametogenesis

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Gametogenesis is a biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of diploid gametocytes into various gametes, or by mitotic division of haploid gametogenous cells. The gametophytes grow from haploid spores after sporic meiosis.

In animalsEdit

Gray7

Scheme showing analogies in the process of maturation of the ovum and the development of the spermatids, following their individual pathways. The oocytes and spermatocytes are both gametocytes. Ova and spermatids are complete gametes. In reality, the first polar body typically dies without dividing.

Animals produce gametes directly through meiosis in organs called gonads. Males and females of a species that reproduces sexually have different forms of gametogenesis:

StagesEdit

However, before turning into gametogonia, the embryonic development of gametes is the same in males and females.

Common pathEdit

Gametogonia are usually seen as the initial stage of gametogenesis. However, gametogonia are themselves successors of primordial germ cells. During early embryonic development, primordial germ cells (PGCs) from the dorsal endoderm of the yolk sac migrate along the hindgut to the gonadal ridge. They multiply by mitosis and once they have reached the gonadal ridge in the late embryonic stage, they are called gametogonia. Gametogonia are no longer the same between males and females.

Individual pathEdit

From gametogonia, male and female gametes develop differently - males by spermatogenesis and females by oogenesis. However, by convention, the following pattern is common for both:

Cell type ploidy/chromosomes chromatids Process
gametogonium diploid/46 2N before replication, 4N after it gametocytogenesis (mitosis)
primary gametocyte diploid/46 2N before replication, 4N after it gametidogenesis (meiosis 1)
secondary gametocyte haploid/23 2N gametidogenesis (meiosis 2)
gametid haploid/23 1N
gamete haploid/23 1N


See alsoEdit



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