The sex chromosomes are the primary genetic factor determining the sex of an individual: a person with two X chromosomes (XX) will be genetically female, a person with one X and one Y (XY) will be genetically male. Some conditions can cause people's apparent gender to differ from their genetic sex.
There are also a number of more unusual chromosomal combinations, including:
- XO: Turner Syndrome
- XXY: Klinefelter syndrome
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