Gametogenesis

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The gametogenesis is the formation of gametes (germ cells) in the context of sex or sexual reproduction .

In humans and in all multicellular animals (Metazoa) it is associated with a reduction division ( meiosis ). With them all body cells are diploid (double set of chromosomes); only the gametes are haploid (simple set of chromosomes) as a result of meiosis and when they are united ( fertilization ) they form a diploid zygote from which the offspring emerges. Such organisms are called diplonts .

In contrast, in haplonts all body cells are haploid, and only the zygote is diploid. In them, gametogenesis is therefore not associated with meiosis. This is the case with many algae . Even in diplohaplons , which are characterized by an alternation of haploid and diploid generations, gametogenesis takes place without meiosis. This includes all (higher) plants .

In animals (and in humans) gametogenesis is called oogenesis in females and spermatogenesis in males .

Gametopathy

Inborn diseases or malformations that are caused by a disruption of gametogenesis are called gametopathy or germ cell damage. These are defects that are already present in the egg cell or sperm cell leading to fertilization. These are either defects that occurred in the course of meiosis or mutations of genes. A congenital defect, the cause of which is not in the gametes but in the later development of the fetus, is called fetopathy .

For example, if a pair of chromosomes does not separate during meiosis (nondisjunction), then the chromosome in question is duplicated in one daughter cell and not at all in the other. In the latter case, the daughter cell usually perishes. If two gametes, one of which contains a double chromosome, fuse during fertilization, this chromosome is present three times in all subsequent cells, which can lead to serious disorders.

Examples of gametopathies due to nondisjunction are trisomy 21 (Down syndrome) and Turner syndrome in humans.

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