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Some women have three, four, or even five X chromosomes per cell. Some women have only one. Some men can also have two or more X chromosomes, in addition to their Y. It's even possible to be biologically female and have the karyotype XY, or be biologically male with an XX karyotype.
The gene for 5-alpha reductase (the male pattern baldness gene) has been mapped to chromosome 5, not the Y chromosome. That means you can get it from any of your ancestors, it just won't show up in the women.
XX and XY chromosomes are not what determines a person's sex - as others have explained, there are many exceptions to that generalisation ... a person's biological sex is determined by the gonads which are present at birth.
XX males that are SRY-positive have two X chromosomes, with one of them containing genetic material (the SRY gene) from the Y chromosome; this gene causes them to develop a male phenotype despite having chromosomes more typical of females. [2]
30 maj 2007 · Now in 1959 when the karyotype of Klinefelter [a male who is XXY] and Turner [a female who has one X] syndromes was discovered, it became clear that in humans it was the presence or the absence...
In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively.
1 wrz 2017 · Beyond XX and XY: The Extraordinary Complexity of Sex Determination. A host of factors figure into whether someone is female, male or somewhere in between. By Amanda Montañez.
