A married couple has four girl children but no boys. This
does not mean that the husband produces only X sperms.
Explain why not.

Explanation:

All children have 'chromosomes' whether the child is girl or boy. Women have XX, Men have XY. Children inherit one piece from each parent. A baby can only receive an X from their mother because their mother only has X. If the baby gets an X from their father, they will have XX and be a girl. If they inherit their fathers Y, they will have XY and be a boy.

So since the Y only can come from their father, this method of inheritance relies on the ability of the father to deliver Y genetic material. A man has two types of sperm. Sperm that is predominantly X carrying and sperm that is predominantly Y. There is a gene(s) that control what sort he produces.

It doesn't mean he doesn't have Y bearing sperm. It just means he may be genetically predisposed to X bearing sperm.