Sex Determination In Human Beings

How does a baby happen to be male or female? The gender of a baby is determined at the time of fertilization only. In the process of fertilization the male gamete or sperm cell unites with the female gamete or the egg cell to form the zygote. The zygote develops into the embryo. The gender of the baby depends on the chromosomal structure of the male and female gametes. The nucleus of the human cell contains 23 pairs or 46 chromosomes out of which 22 pairs are called autosomes that determine the physical traits and the remaining one pair of chromosomes is called allosomes or sex chromosomes. This pair of sex chromosomes determines the gender of the baby. The pair of sex chromosomes is designated as XY in males and as XX in females.

In the formation of sperm cells and egg cell a special division called Meiosis occurs due to which the number of chromosomes in the sperm cell and the egg cell is reduced to half. That means the egg cell contains 23 chromosomes (22 + X). All the sperm cells formed due to the Meiotic division contain 23 chromosomes each but they will be of two kinds. 50% of the sperm cells contain (22 + X) chromosomes while the other 50% of them contain (22 + Y) chromosomes. In the process of fertilization if the sperm cell with the X chromosome happens to unite with the egg cell the zygote will have XX chromosomes which will develop into a female baby and if the sperm cell with Y chromosome happens to unite with the egg cell the zygote will have XY chromosomes which will develop into a male baby. So to be a male or a female is purely a chance factor.