Question

Explain the mechanism of sex determination in humans with a suitable chart.

Answer 1

Sex Determination in human being:

1. The chromosomal mechanism of sex determination in human beings is of the XX – XY type. The human diploid cell has 23 pairs of chromosomes.
2. Out of these, 22 pairs of chromosomes are called autosomes, and one pair of chromosomes is called sex chromosomes that are responsible for the determination of sex.
3. The human female has a pair of XX, homomorphic sex chromosomes while the male has XY, heteromorphic sex chromosomes.
4. A human male has 44 autosomes + XY sex chromosomes, whereas a female has 44 autosomes + XX sex chromosomes.
5. During gamete formation in males, the diploid germ cells in testis undergo spermatogenesis to produce two types of haploid sperms, 50% of sperms contain 22 autosomes and X chromosome while 50% of sperms contain 22 autosomes and the Y chromosome.
6. In females, the diploid germ cells in ovaries undergo oogenesis to produce only one type of egg. All eggs contain 22 autosomes and an X chromosome.
7. Thus human male is heterogametic and the female is homogametic.
8. If sperm containing the X chromosome fertilizes the egg (ovum), the diploid zygote formed after fertilization grows into a female child.
9. If sperm containing the Y chromosome fertilizes the egg, then the diploid zygote formed after fertilization grows into a male child.
10. The sex of a child depends on the type of sperm fertilizing the egg and hence the father is responsible for the determination of the sex of the child and not the mother.