During puberty, a change in the voice of boys and girls takes place due to increase in the size of the voice box or larynx. In boys, the voice box tends to protrude out on the upper part of the neck, below the chin and is often referred to as Adam’s apple.
(b) Secondary sexual characters.
Those characters which are visible more apparently and help in distinguishing a male from a female are called secondary sexual characters. For example, in girls, breasts and in boys, facial hair, i.e., moustache and beard.
(c) Sex determination in the unborn baby.
The sex of a baby is determined by the type of male gamete that fuses with the female gamete.All human beings have 23 pairs of chromosomes in their nuclei. Out of these 23 pairs, the last pair is known as the sex
chromosome. The human males have 23 pairs of chromosomes including XY sex chromosomes. Therefore, the male gamete has 22 chromosomes and either an X or Y sex chromosome. Male gametes can be of two types: 22+X or 22+Y. Females have 23 pairs of chromosomes including XX sex chromosomes. Therefore, their gametes can only have 22 chromosomes and one X sex chromosome. Type of female gametes: 22+X
Thus, as the mother provides only X chromosome, the sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.