Correct Option (D)
Assertion (A) states that in human beings, females play a major role in determining the sex of the offspring. This assertion is false. In humans, males possess XY sex chromosomes, while females possess XX sex chromosomes. During reproduction, females contribute an X chromosome to the offspring. Males, however, can contribute either an X or a Y chromosome. If the male contributes an X chromosome, the offspring will be female (XX). If the male contributes a Y chromosome, the offspring will be male (XY). Therefore, the male gamete determines the sex of the offspring.
Reason (R) states that women have two ‘X’ chromosomes. This reason is true. Human females are characterized by having two X chromosomes (XX) in their somatic cells, which is the standard chromosomal complement for biological sex determination in females.
Incorrect Options:
Options A, B, and C are incorrect because Assertion (A) is false. The male, not the female, determines the sex of the offspring in humans due to the presence of both X and Y chromosomes in males, whereas females only contribute X chromosomes.