Science Common Sense

1281 - What determines human sex.

Human sex is determined by chromosomes, which are tiny parts inside our cells that carry genetic information.

Humans have 23 pairs of chromosomes, for a total of 46. One of these pairs, called the sex chromosomes, can be either XX (two X chromosomes) or XY (one X and one Y chromosome).

• XX usually makes a person female.
• XY usually makes a person male.

This usually happens because of the following:

• A mother has two X chromosomes (XX) in her cells, so she can only give her baby an X chromosome.
• A father has one X and one Y chromosome (XY) in his cells, so he can give his baby either an X or a Y chromosome.

If the baby gets an X from mom and an X from dad, the baby is XX and usually a female. If the baby gets an X from mom and a Y from dad, the baby is XY and usually a male.

That's how our chromosomes help decide if we are male or female.