Question

Assertion (A) : The human blood group "AB" exemplifies co-dominance.

Reason (R) : The gene for human blood group trait exists in three allelic forms \( \mathrm{I^{A}} \), \( \mathrm{I^{B}} \) and i.

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

Hint:

Group AB shows co-dominance, and three alleles show multiple allelism; the second fact does not explain the first.

Answer 1

The Correct Option is B

Step 1: Check the Assertion:
A person with genotype \( \mathrm{I^{A}I^{B}} \) has both A and B antigens on the red cells. Both alleles express fully.
This is co-dominance, so A is true.

Step 2: Check the Reason:
The ABO gene has three alleles: \( \mathrm{I^{A}} \), \( \mathrm{I^{B}} \) and i. This is multiple allelism, so R is true.

Step 3: Decide if R explains A:
Having three alleles does not by itself give co-dominance. Co-dominance is shown only when two alleles in one person both express, like \( \mathrm{I^{A}} \) and \( \mathrm{I^{B}} \).
The Reason describes multiple allelism, and it is not the explanation of the Assertion.

Step 4: Pick the code:
Both statements are true, but R does not explain A. That is option (B).

Final Answer:
Option (B) is correct. \[ \boxed{\text{(B)}} \]