How is the sex of the child fixed during the fertilisation step in human beings? Explain.
In humans, the sex of child is determined at time of fertilization when male and female gametes fuse to form zygote. See the following terms as:
(i) If a sperm carrying X chromosome fertilises an ovum which carries X chromosome then the child born will be a girl XX.
(ii) If a sperm carrying Y chromosome fertilises an ovum which carries X chromosome then the child born will be a boy XY.
Thus, the sperm determines the sex of the child.
