Question

Answer the following questions related to sex determination in human beings:
i. What is sex chromosome?
ii. How many pairs of chromosomes are present in human beings?
iii. How is the sex of the human offspring determined?
iv. Draw a diagram depicting sex determination in man.

Answer 1

i. The sex chromosome is a chromosome involved in sex determination.

ii. 23 pairs of chromosomes are present in human beings. Of these, 22 pairs are of the autosomes and 1 pair is of the sex chromosomes.

iii. Determination of sex in human offspring:

1. In human beings, the male possesses 44 autosomes and a pair of heteromorphic sex chromosomes, XY, while the female possesses 44 autosomes and a pair of homomorphic sex chromosomes, XX.
2. At the time of gamete formation, meiosis occurs.
3. The male parent produces X-bearing and Y-bearing gametes or sperms. The female parent produces only X-bearing gametes or eggs.
4. During reproduction, the combination of one X-bearing gamete from the male with one X-bearing gamete from the female results in offspring with the genetic constitution XX. The child produced is a female or a daughter.
5. The combination of a Y chromosome from the male with one X chromosome from the female results in an offspring with genetic constitution XY. The child produced is a male or a son.
6. The offspring produced are always in equal proportion, and hence, the chance of having a daughter or a son is 50%.

iv. Sex determination in man: