Answer:
1. A human body has 23 pairs of chromosomes out of which 2 pairs are sex chromosomes.
2. Male has X and Y chromosomes whereas the female has both X chromosomes.
3. The baby inherits an X chromosome from mother and X or Y chromosome for father.
4. If a baby inherits X from father then the baby will be a girl and if inherits Y then that baby will be a boy.
5. In such a way, sex of the child is determined and it is always determined by the father only.