CBSE Class 10 Science 2022 · Paper 31/3/1 · Question 6(b)

A woman has a perfect pair of sex chromosomes, $XX$, and a man a mismatched pair, $XY$. So every egg carries an $X$ chromosome, while half the sperms carry an $X$ and half carry a $Y$. If a sperm carrying $X$ fertilises the egg, the child is $XX$, a girl; if a sperm carrying $Y$ fertilises it, the child is $XY$, a boy. Since the mother always contributes an $X$, the sex of the child is decided by whether it inherits an $X$ or a $Y$ from its father, which justifies the statement.