Each point: 1 Mark
1. Sex of an unborn baby depends upon the pair of sex chromosomes that are present in the cells of the baby. The two sex chromosomes are X and Y.
2. The unfertilized egg always has one X chromosome. But sperms are of two kinds. One kind has an X chromosome, and the other kind has a Y chromosome.
3. If both the chromosomes are X then the baby is a girl. If one of the chromosomes is X and the other is Y then the baby is a boy.