Question

Assertion : In humans, the gamete contributed by the male determines whether the child produced will be male or female.
Reason : Sex in humans is a polygenic trait depending upon a cumulative effect of some genes on X-chromosome and some on Y-chromosome.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (C)

Sex chromosomes in the human female are XX; whereas those of the male are XY. During the very early stages of gestation period, the development of the embryo is predisposed in certain directions by the possession of the sex chromosomes one contributed by the mother and the other by the father. The mother can contribute only X chromosome which predisposes towards the development of female structural, functional and temperamental characteristics, but the father can contribute either an X or a Y chromosome predisposing in the first instance to female or in the second to male structural, functional and temperamental characteristics. In short, the sex of the child to be born is governed by the chromosomal contribution of the father. A child conceived will develop into a female on receiving an X chromosome from the mother and an X chromosome from the father (XX), or into a male on receiving an X chromosome from the mother but a Y chromosome from the father (XY). Therefore, sex in humans is not polygenic.