Question

Explain how sex is determined in human babies.

Answer 1

Humans contain ${\text{23}}$pairs of chromosomes, the ${\text{2}}{{\text{3}}^{{\text{rd}}}}$pair are the sex chromosomes (which determine the sex whether the offspring will be male or female).

Complete answer:
In human beings, the sex of a child is determined depending upon which type of male gamete (i.e. XY) fertilizes with the female gamete (i.e. XX). In each of the mother and father, there are $23$ pairs of chromosomes out of which $22$pairs are Autosomes and only one pair i.e. ${\text{2}}{{\text{3}}^{{\text{rd}}}}$is the sex chromosome which actively takes part in the process of sex determination. Both males and females carry two sets of sex chromosomes; a male (XY) has one X and one Y sex chromosome in which one is active while a female (XX) has both X sex chromosomes in which one is active.
During the time of fertilization, sperm fertilizes the egg cell to form a zygote. If sperm carrying X-chromosome fertilizes an ovum carrying an X chromosome, then the sex of the child born will be a girl (XX) and if sperm carrying the Y-chromosome fertilizes an ovum carrying an X chromosome then the sex of the child will be a boy (XY).

Additional information:
- Autosomes are chromosomes that are the same in both sexes.
- Sex chromosomes are also termed allosomes.
- Males are called heterogametic because they have Y-chromosomes.

Note: The XY sex-determination system is present in humans, mammals, in some insects, and in few plant species. A child who inherits the Y chromosome will be a boy and who inherits the X chromosome will be a girl. Sex is the hereditary difference between two individuals of the same species.