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How is a persons sex determined?

A person's sex is determined by the complement of sex chromosomes. Humans normally have two sex chromosomes. Females have two X chromosomes, and males have one X and one Y chromosome. Rarely, a person might be born with three sex chromosomes. A person with XXY is a male, indicating that the presence of a Y chromosome (as opposed to the presence of only one X) confers maleness. Presumably there is a master regulatory gene on the Y chromosome that confers male sexual identity. In the absence of this gene, the fetus will develop as a female.


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