Q1. [1] § 8.1 ACCUMULATION OF VARIATION DURING REPRODUCTION § 8.2 HEREDITY § 8.2.2 Rules for the Inheritance of Traits – Mendel's Contributions
Assertion (A) : In humans, if gene (B) is responsible for black eyes and gene (b) is responsible for brown eyes, then the colour of eyes of the progeny having gene combination Bb, bb or BB will be black only.
Reason (R) : The black colour of the eyes is a dominant trait.
- (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.
Previously asked in CBSE board exam
2023 31/4/1 Q18
Generated by claude-sonnet-4-6 · 2026-06-15 06:52 · grounding rag
Model Answer
(d) (A) is false but (R) is true.
Assertion is false because progeny with bb (homozygous recessive) will have brown eyes, not black. Reason is true — black eye colour (B) is the dominant trait.
Explanation
- The key error in Assertion (A) is including bb: since 'b' is recessive, bb gives brown eyes, not black.
- BB and Bb both give black eyes (dominant trait expressed), but bb gives brown eyes.
- Reason (R) is correctly stated — dominance of B explains why BB and Bb show black eyes, but it does not save the Assertion from being false.
- So the correct option is (d).
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