Answer: Adam’s apple: 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 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, chest hair. (c) Sex determination in the unborn baby: The sex of a child, is determined at the time of fertilisation when a male gametes fuses with a female gamete. All human beings have 23 pairs of chromosomes. 2 chromosomes out of these are sex chromosomes. A female has two X chromosomes, while a male has one X and one Y chromosome. The gamete cells have only one set of chromosomes. The unfertilised egg has one X chromosome. But sperms maybe of two kinds— One having X chromosome, and the other having Y chromosome. When a sperm containing X chromosome fertilises the egg, the zygote would have two X chromosomes and develop into a female child. If the sperm contributes a Y chromosome to the egg or ovum at fertilisation, the zygote would develop into a male child. It is thus also clear that the sex chromosomes of the father determine the sex of an unborn baby.