The chromosome pattern in the human female is XX and that in the
male is XY. Therefore, all the gametes (ova) produced by the female have
the sex chromosome X whereas in the male gametes (sperms) the sex
chromosome could be either X or Y. Hence, 50 per cent of sperms carry
the X chromosome while the other 50 per cent carry the Y. After fusion
of the male and female gametes the zygote would carry either 'XX or 'XY
depending on whether the sperm 'X or 'Y fertilized the ovum. The zygote
carrying XX would develop into a female baby and XV would form a male.
That is why, scientifically it is correct to say that the sex of the
baby is determined by the father and not by the mother.