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'Gametogenesis' is the creation of gametes. Depending on the biological life cycle of the organism, gametogenesis occurs by meiotic division of gametocytes into various gametes or by mitotic division of haploid gametogenous cells. For example, plants produce gametes through mitosis in gametophytes. The gametophytes grow from haploid spores after sporic meiosis. The existence of a multicellular, haploid phase in the life cycle between meiosis and gametogenesis is also referred to as alternation of generations.

Contents

Gametogenesis in animals

Stages

Common path

Individual path

Gametogenesis in gametangia

Gametogenesis in flowering plants

Gametogenesis in animals

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

★ 'spermatogenesis' (male)

★ 'oogenesis' (female)

Stages

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

Common path

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 they are called gametogonia. Gametogonia are not longer the same between males and females.

Individual path

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	gametocytogenesis (mitosis)
primary gametocyte	diploid/46	4N	gametidogenesis (meiosis 1)
secondary gametocyte	haploid/23	2N	gametidogenesis (meiosis 2)
gametid	haploid/23	1N
gamete	haploid/23	1N

Gametogenesis in gametangia

Fungi, algae and primitive plants form specialized haploid structures called gametangia where gametes are produced through mitosis. In some fungi, for example zygomycota, the gametangia are single cells on the end of hyphae and acting as gametes by fusing into a zygote. More typically, gametangia are multicellular structures that differentiate into male and female organs:

★ 'antheridium' (male)

★ 'archegonium' (female)

Gametogenesis in flowering plants

In flowering plants, the male gamete is produced inside the pollen grain through the division of a generative cell into two sperm nuclei. Depending on the species, this can occur while the pollen forms in the anther or after pollination and growth of the pollen tube. The female gamete is produced inside the embryo sac of the ovule.