Determination of Sex

In humans, one pair of chromosomes (the 23rd pair) determines the gender of the individual. These 2 chromosomes are known as the sex chromosomes.

The X chromosome is larger and carries more genes than the Y chromosome (See diagram above.).

If two X chromosomes (XX) are present in the embryo, it generally develops into a female.

If one X and Y (XY) are present in the embryo, it generally develops into a male.

Males determine the sex of the offspring as they can create either an X sperm or a Y sperm. If a Y sperm fertilizes an egg, the embryo becomes a male. If an X sperm fertilizes an egg, the embryo becomes a female.

Females can only create X eggs.