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.

• 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.

Hint:

In humans, males are heterogametic (XY), while in birds, females are heterogametic (ZW).

Answer 1

The Correct Option is C

Step 1: In humans and many other organisms, the XX–XY system shows male heterogamety where males produce two types of gametes (X and Y), so Assertion (A) is true.
Step 2: However, in birds, females are the heterogametic sex (ZW), and males are homogametic (ZZ), making Reason (R) false.
Step 3: Since (R) is incorrect, it cannot explain (A).
Thus, (A) is true, but (R) is false.