Assertion–Reason (Genetics – Color Blindness): Assertion (A): Red–green color blindness occurs more frequently in males than in females. Reason (R): Females have two X chromosomes, whereas males have only one.
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ABoth A and R are true, and R is the correct explanation of A
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BBoth A and R are true, but R is not the correct explanation of A
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CA is true but R is false
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DA is false but R is true
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ENone of these
Answer
Correct Answer: Both A and R are true, and R is the correct explanation of A
Explanation
Introduction / Context:The question examines understanding of X-linked recessive inheritance using red–green color blindness as the classic example.
Given Data / Assumptions:
- Trait occurs more in males.
- Chromosomal complement: males XY; females XX.
Concept / Approach:In X-linked recessive traits, a single mutant allele on the X chromosome is sufficient to express the phenotype in males (XY). Females (XX) would need two mutant alleles to express the condition; with only one mutant allele they are typically carriers without full expression, reducing prevalence among females.
Step-by-Step Solution:1) A: True—statistically, males show higher incidence.2) R: True—chromosomal complement explains hemizygous exposure in males.3) The reason directly explains the observation in A.
Verification / Alternative check:Pedigree patterns show affected males more frequently and transmission via carrier mothers; father-to-son transmission does not occur for X-linked traits.
Why Other Options Are Wrong:They deny either the epidemiological pattern or the genetic mechanism.
Common Pitfalls:Assuming dominance or autosomal inheritance; overlooking carrier females.
Final Answer:Both A and R are true, and R explains A.