The sex of a baby is determined at the time of conception by the combination of sex chromosomes from the parents. The mother always provides an X chromosome through her egg, while the father provides either an X or a Y chromosome through his sperm.
- If the sperm carries an X chromosome, the baby will be a girl (XX).
- If the sperm carries a Y chromosome, the baby will be a boy (XY).
Therefore, it is the father’s chromosome that decides the sex of the baby.
