Question

Of the following statements, which is/are correct?
(A) During incomplete dominance, the modified allele is the dominant allele
(B) In polygenic inheritance, the effect of each allele is additive
(C) A gene is called pleiotropic when it exhibits multiple phenotypic expressions
(D) Mutation means alteration of DNA sequence which ensures change only in the phenotype of an organism
Choose the correct answer from the options given below:

• A. (A), (B), and (C) only
• B. (B) and (C) only
• C. (D) only
• D. (C) and (D) only

Answer 1

The Correct Option is B

Let’s evaluate each statement:

(A) During incomplete dominance, the modified allele is the dominant allele: This is incorrect. In incomplete dominance, neither allele is completely dominant. Instead, the phenotype is a blend of the two alleles, such as in the case of red and white flowers producing pink flowers.

(B) In polygenic inheritance, the effect of each allele is additive: This is correct. In polygenic inheritance, multiple genes contribute to the expression of a trait, and the effects of these alleles are typically additive. This results in continuous variation, such as in human skin color or height.

(C) A gene is called pleiotropic when it exhibits multiple phenotypic expressions: This is correct. Pleiotropy refers to a situation where a single gene influences multiple, seemingly unrelated phenotypic traits. For example, the Marfan syndrome gene affects connective tissues and can influence eye shape, limb length, and heart health.

(D) Mutation means alteration of DNA sequence which ensures change only in the phenotype of an organism: This is incorrect. Mutations are changes in the DNA sequence, but they do not always lead to a change in the phenotype. Many mutations are silent, meaning they do not alter the phenotype. Additionally, not all mutations affect phenotype directly.

The correct answer is (2) (B) and (C) only.

 

Answer 2

Statement (B) is correct because, in polygenic inheritance, the effect of each allele is additive, meaning multiple alleles collectively influence the trait. Statement (C) is also correct; a gene is termed pleiotropic when it has multiple phenotypic effects. Statement (A) is incorrect because incomplete dominance involves a blending of traits, where neither allele is fully dominant. Statement (D) is incorrect since mutation can alter both genotype and phenotype, not necessarily affecting only the phenotype.