What determines the sex of a child?

Like every other animal, the human beings are also divided into two sexes — male and female. Why are some babies born as girls and others as boys? In other words, what determines the sex of an individual? A woman becomes capable of bearing a child after she starts menstruating. Between the 10th and the 18th days from the onset of menstruation, the reproductive organs of a woman produce an egg called ‘ovum‘. During this period if a woman mates with a man, a sperm present in the semen of the man fertilises the egg. The ovum and the sperm then combine resulting in the formation of an embryo. The ova of the female and the sperms of the male contain sex chromosomes. The ova have only one type of chromosomes called X-chromosomes. But the sperms have two types of sex chromosomes called X and Y-chromosomes respectively. The X-chromosomes are slightly bigger than the Y-chromosomes in size. When female sex cells are to be formed, the two Xchromosomes of the female germ cell come together. They then split lengthwise, forming four X-chromosomes. In the formation of male sex cells, the single X-chromosome pairs with its smaller partner, the Y-chromosome. Each of these chromosomes split lengthwise. The cell then contains two X-chromosomes and two Y-chromosomes. When this cell gives rise to four new cells — the sex cells — half will contain X-chromosomes, the other half, Y-chromosomes. If the X-chromosome fertilises the egg, the child would be a female, but on the other hand if a cell containing Y-chromosome fertilises the ova, the offspring would be a male. As a matter of fact, male births are slightly more frequent than female births