Question

Consider the following statements
Assertion (A): Skin colour in human beings is a polygenic trait.
Reason (R): Human skin colour is controlled by cumulative effect of genes.
The correct answer is

• A. Both (A) and (R) are true, (R) is the correct explanation of (A)
• B. Both (A) and (R) are true, (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:

Polygenic inheritance shows a continuous variation (Bell-shaped curve) in the population, unlike Mendelian traits which are distinct.

Answer 1

The Correct Option is A

Step 1: Analyze Assertion (A):
Skin colour in humans is controlled by three (or more) pairs of genes (usually denoted as A, B, C). Traits controlled by multiple genes are called Polygenic traits (or Quantitative inheritance). Thus, (A) is true.
Step 2: Analyze Reason (R):
In polygenic inheritance, each dominant allele contributes a small amount to the phenotype (e.g., melanin production). The final phenotype is the result of the additive or cumulative effect of all the dominant alleles present in the genotype. For example, AABBCC is darkest, aabbcc is lightest, and AaBbCc is intermediate. This mechanism (cumulative effect) is the definition and explanation of how a polygenic trait works. Thus, (R) is true and explains (A).