How is the sex of the child determined in human beings?

A baby's sex depends on the father's sperm. If a sperm carrying an X chromosome fertilises the egg (which always has an X), the baby is a girl (XX). If a sperm with a Y chromosome fertilises the egg, the baby is a boy (XY).

Sex determination in humans follows the chromosomal mechanism: 1. Humans have 23 pairs of chromosomes — 22 pairs are autosomes and 1 pair are sex chromosomes. 2. Females have two X chromosomes (44 + XX). All eggs produced by a female carry 22 autosomes and one X chromosome (22 + X). 3. Males have one X and one Y chromosome (44 + XY). Males produce two types of sperm in equal proportion — 50% carry 22 + X and 50% carry 22 + Y. 4. During fertilisation, if an X-bearing sperm fuses with the egg (X), the zygote is XX (female). If a Y-bearing sperm fuses with the egg (X), the zygote is XY (male). 5. Therefore, the sex of the child depends entirely on which type of sperm fertilises the egg. The father determines the child's sex — the mother's egg always contributes an X chromosome.