Ans. In humans, the determination
of sex can be done due to the presence
of XX-XY chromosomes in female and male respectively. Human beings have
46 chromosomes which are distinguished into 22 pairs of autosomes and one pair of sex-chromosomes.
Human female has 44 autosomes + XY sex-chromosomes while male has autosomes sex-chromosomes. +XY
Male (man) has X and Y type sex-chromosomes and produces two
types of male gametes or sperms.
50% of the sperms carry X-chromosome and the other 50% carry Y-chromosome, hence males (men) are heterogametic.
The females (women) carry both the same type XX sex-chromo somes and produce only one type of gametes (eggs or ovum), hence called homogametic. All the eggs bear only one, i.e., 'X'. type of chromosome.
When the male's sperm bearing X-chromosome fuses with egg (ovum) during fertilisation to form zygote.
Such zygote develops into a female baby having XX sex-chromosomes.
If male's sperm bearing Y-chromosome fuses with egg to form zygote, this zygote gives birth to a male baby having XY sex chromosome.
Thus, in humans, there is 50 percent chances of a boy and 50 percent chances of a girl to be borne in an offspring of the parents. In human, it is the sperm which determines the sex of the child.
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