Question

Assertion (A): Human female has a perfect pair of sex chromosomes.
Reason (R): Sex chromosome contributed by the human male in the zygote decides the sex of a child.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true, but (R) is not the correct explanation of (A).
• C. (A) is true, but (R) is false.
• D. (A) is false, but (R) is true.

Answer 1

The Correct Option is B

Step 1: Evaluate Assertion (A):
Assertion (A) states that a human female possesses a perfect pair of sex chromosomes. This is accurate because human females have two X chromosomes (XX), which are structurally identical. Thus, this assertion is true. The two X chromosomes in females are considered a "perfect pair" due to their homology, meaning they carry similar genetic information related to female characteristics.

Step 2: Evaluate Reason (R):
Reason (R) posits that the sex chromosome contributed by the human male to the zygote determines the child's sex. This statement is also true. The sex of a child is determined by the male's genetic contribution, as the female can only contribute an X chromosome (owing to her XX sex chromosomes). The male, however, can contribute either an X or a Y chromosome. If the male contributes an X chromosome, resulting in XX, the child will be female. If the male contributes a Y chromosome, resulting in XY, the child will be male. Therefore, the male's sex chromosome is the determinant of the child's sex.

Step 3: Analyze the Relationship between Assertion and Reason:
Although both the assertion and the reason are factually correct, Reason (R) does not directly elucidate Assertion (A). The presence of a perfect pair of sex chromosomes (XX) in a female is an intrinsic biological characteristic and is not dictated by the male's contribution. The male's contribution, which determines the child's sex, is independent of the concept of a "perfect pair" of sex chromosomes in females. Consequently, Reason (R) does not serve as a valid explanation for Assertion (A).

Step 4: Conclusion:
The correct response is: Both (A) and (R) are true, but (R) is not the correct explanation of (A). While both statements are accurate, Reason (R) explains sex determination but does not explain why a female has a "perfect pair" of sex chromosomes.