What determines whether a baby is a boy or a girl?

The sex of the baby is determined by the chromosomes. Usually, all of us have 23 pairs of chromosomes. They determine how our body looks like and how it works. They are also the reason we resemble our parents. The 23rd pair of chromosomes is different in case of males and females. In a woman, these are two X chromosomes, in a man it is one X and one Y chromosome. The egg cell has an X chromosome; the sperm could have either an X or a Y chromosome. If a sperm with a ‘Y’ chromosome fertilizes the egg, then the chromosome combination for the baby would be XY: a boy. If an ‘X sperm’ fertilizes the egg, the result is XX: a girl. It is clear, therefore, that the sex of the baby is determined by the father.