When there is an increase in the size of the larynx during puberty, it sticks out at the front of the throat. Everyone's larynx grows during puberty, but a girl's larynx doesn't grow as much as a boy's larynx grows. As boys' larynx grows more, it makes their voices deeper than girls' voice. In boys, the voice box tends to protrude out on the upper part of the neck, below the chin and is referred as Adam’s apple.
(b) Secondary sexual characters.
Secondary sexual characteristics are the features that appear during puberty in humans, and at sexual maturity in other animals. These characters are visible more apparently and thus help in distinguishing a male from a female. In humans, visible secondary sexual characteristics include pubic hair, enlarged breasts and widened hips in females and facial hair and Adam's apple in males.
(c) Sex determination in the unborn baby.
Every human has two types of chromosomes i.e., autosomes and sex chromosomes. There are 22 autosomes and 2 types of sex chromosomes i.e., X and Y. There is a total of 23 pairs of chromosomes in an individual.
A male individual has 44 autosomes and XY sex chromosomes while a female individual has 44 autosomes and XX sex chromosomes.
So if a male gamete(sperm) containing 22 autosomes and X chromosome fuses with a female gamete(ova/egg) containing 22 autosomes and X chromosome, then the zygote contains a total of (44 + XX) chromosomes, thus later forming a female child.
And if a male gamete(sperm) containing 22 autosomes and Y chromosome fuses with a female gamete(ova/egg) containing 22 autosomes and X chromosome, then the zygote contains a total of (44 + XY) chromosomes, thus later forming a male child.
As the sex of a child depends on the type of male gamete containing either X or Y chromosome, hence the sex determination of a child depends on the father.