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

To determine which statements are correct, we will evaluate each one based on biological principles: 

(A) During incomplete dominance, the modified allele is the dominant allele: Incomplete dominance actually refers to a situation where neither allele is completely dominant over the other. Instead, the phenotype is a blend of the two alleles. Hence, statement (A) is incorrect.

(B) In polygenic inheritance, the effect of each allele is additive: Polygenic inheritance involves several genes contributing to a trait, with each allele adding a small amount to the phenotype. Thus, statement (B) is correct.

(C) A gene is called pleiotropic when it exhibits multiple phenotypic expressions: Pleiotropy occurs when one gene influences multiple phenotypic traits. Therefore, statement (C) is correct.

(D) Mutation means alteration of DNA sequence which ensures change only in the phenotype of an organism: Mutation involves changes in the DNA, but it does not guarantee a change in phenotype; it depends on many factors. Thus, statement (D) is incorrect.

Based on this analysis, the correct statements are (B) and (C) only.

Answer 2

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.