"The sex of a newborn child is a matter of chance and none of the parents may be considered responsible for it." Justify this statement with the help of a flow chart showing determination of sex of a newborn.

Explanation

Sex determination flow chart:
(i) A male has one X- chromosome and one Y-chromosome. Thsu half the male gametes have X-chromosomes and the other half have Y-chromosomes.
(ii) A female has two X-chromosomes. Thus all female gametes have only X-chromosomes.
(iii) If a sperm carrying Y-chromosome fertilises an ovum carrying X-chromosome, then the child born will be a boy.
(iv) If a sperm carrying X-chromosome fertilises an ovum carrying X-chromosome, then the child born will be a girl.

Therefore it is the sperm from the father which determines the sex of the child.
Thus in human geings, the sex of the baby is determined by the type of sperm that fuses with ovum. As human male produces two types fo sperms in equal proportion, so there are `50%` chances of a male baby and `50%` chances of a female baby.