CBSE 2025, Set 2

Question

Assertion (A): XX-XY type of sex-determination mechanism is an example of male heterogamety.
Reason (R): In birds male heterogamety is observed as males produce two different types of gametes.

Select the correct option: 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.

Edvaya · Accepted Answer

The correct answer is (A) is true, but (R) is false.. **SOLUTION** **Assertion (A) is True:** The XX-XY mechanism (seen in humans and Drosophila) is an example of male heterogamety because males produce two different types of gametes (X and Y). **Reason (R) is False:** In birds, sex determination follows the ZZ-ZW mechanism. In this system, females produce two different types of gametes (Z and W), making it an example of **female heterogamety**. Males are homogametic (ZZ).

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Biology > Reproduction And Genetics > Principles Of Inheritance And Variation

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