Sex change hormones online

the origin of chromosomal sex determination may have been fairly early in eukaryotes (see Evolution of anisogamy).The ZW sex-determination system is shared by birds, some fish and some crustaceans.Many species, particularly animals, have sexual specialization, and their populations are divided into male and female individuals.

In sexual reproduction, the genetic material of the offspring comes from two different individuals. Sexual reproduction involves the combining and mixing of genetic traits: specialized cells known as gametes combine to form offspring that inherit traits from each parent.Gametes can be identical in form and function (known as isogamy), but in many cases an asymmetry has evolved such that two sex-specific types of gametes (heterogametes) exist (known as anisogamy).This double-chromosome stage is called "diploid", while the single-chromosome stage is "haploid".Diploid organisms can, in turn, form haploid cells (gametes) that randomly contain one of each of the chromosome pairs, via meiosis.

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XY sex determination is used by most mammals, and from a comparison between chicken and human, the Z chromosome appeared similar to the autosomal chromosome 9 in human, rather than X or Y, suggesting that the ZW and XY sex-determination systems do not share an origin, but that the sex chromosomes are derived from autosomal chromosomes of the common ancestor of birds and mammals.

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