(a) by ovum(b) at the time of fertilisation(c) 40 days after fertilisation(d) seventh to eight week when genitals differentiate in foetus[CBSE AIPMT 1993]
Correct Option (b) Reason : In human beings male produces two types of sperms. 50% of them carry X-chromosome and 50% have Y-chromosome.
Sex in human beings is determined at the time of fertilisation because sex of baby depends upon which sperm fertilises the ovum.