Nondisjunction of the X chromosome can produce sex chromosome aneuploidies.
In humans, the presence of a Y chromosome determines gender and makes the individual male.
- XXX individuals are females: the extra X is usually inactivated.
- Turner syndrome (XO) individuals are females: missing the small Y is survivable.
- Klinefelter syndrome (XXY) individuals are males: the extra X is usually inactivated.
- OY individuals are nonviable: missing the large X is fatal.
