sex determinationExperiments involving the removal of the embryonic gonad have revealed that in mammals, no matter what the chromosomal sex of the somatic cells, the body will develop as a female unless a male gonad is present to secrete mullerian inhibiting substance and testosterone. This can be partially mimicked in the genetic condition testicular feminisationin which the gene coding for the androgen receptor is not expressed so that, although the testis in an XY individual secretes testosterone, the somatic tissues are unable to respond to it. Consequently the individual's body develops as a woman but with internal testes instead of ovaries. In 1990, a Y encoded gene SRYwas discovered which (at least in mice) is able to transform the sex of an XX embryo from female to male. Individuals with mutations in this gene develop as females despite having an XY chromosomal constitution. About one male in 10,000 does not appear to have anY chromosome but instead has two X chromosomes. These
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XY sex-determination system, Gamete, Y chromosome