Question

Match LIST-I with LIST-II

Choose the correct answer from the options given below:

• A. A-I, B-II, C - III, D - IV
• B. A-II, B-I, C - IV, D - III
• C. A-IV, B - III, C - II, D-I
• D. A-III, B - IV, C - I, D - II

Hint:

To quickly recall these ratios, remember the totals. Complementary (9+7=16), Recessive Epistasis (9+3+4=16), Dominant Epistasis (12+3+1=16), and Inhibitory (13+3=16). Associate Complementary with 9:7 and Dominant Epistasis with 12:3:1 as the most common examples.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
This question tests the knowledge of different types of gene interactions (epistasis) and their characteristic modified Mendelian F2 dihybrid ratios. The standard dihybrid ratio is 9:3:3:1.
Step 2: Detailed Explanation:
Let's match each type of gene interaction with its resulting F2 ratio:


A. Complementary gene action: Both dominant genes (e.g., A and B) are required to produce a particular phenotype. The absence of either dominant gene results in a different phenotype. Genotypes A_B_ produce one phenotype, while A_bb, aaB_, and aabb produce another. This combines the 3, 3, and 1 parts of the ratio, leading to a 9:7 ratio. This matches IV.

B. Supplementary gene action (Recessive Epistasis): A recessive allele at one locus (e.g., aa) masks the expression of alleles at another locus. For example, A_B_ (phenotype 1), A_bb (phenotype 2), but aaB_ and aabb are both phenotype 3. This combines the 3 and 1 parts, leading to a 9:3:4 ratio. This matches III.

C. Inhibitory gene action: A dominant allele at one locus (the inhibitor gene, I) prevents the expression of a dominant allele at another locus. For example, I_C_ and I_cc are one phenotype (e.g., white), iiC_ is the second phenotype (colored), and iicc is also the first phenotype (white). This combines the 9, 3, and 1 parts, leading to a 13:3 ratio. This matches II.

D. Masking gene action (Dominant Epistasis): A dominant allele at one locus (e.g., A) masks the expression of alleles at another locus. For example, A_B_ and A_bb produce one phenotype, aaB_ produces a second, and aabb produces a third. This combines the 9 and 3 parts, leading to a 12:3:1 ratio. This matches I.

Step 3: Final Answer:
The correct matching is A-IV, B-III, C-II, D-I.