The recombination frequency between the genes a & c is 5%, b & c is 15%, b & d is 9%, a & b is 20%, c & d is 24% and a & d is 29%. What will be the sequence of these genes on a linear chromosome?
Answer: (D) a, c, b, d. Answer: (D) a, c, b, d Solution: Recombination frequency is proportional to map distance, so genes are ordered by adding distances.
- A.a, d, b, c
- B.d, b, a, c
- C.a, b, c, d
- D.a, c, b, d✓
Correct Answer
(D) a, c, b, d
Solution & Explanation
Answer: (D) a, c, b, d Solution: Recombination frequency is proportional to map distance, so genes are ordered by adding distances. Given a-c = 5, c-b = 15 (so a-b = 20, consistent), b-d = 9, and a-d = 29 (= 5 + 15 + 9), the linear order is a - c - b - d. This matches option D; the largest distance (a-d, 29%) correctly spans the two ends. NCERT Reference: NCERT Class XII, Ch 4, p.67, lines 47-50: "His student Alfred Sturtevant used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes and 'mapped' their position on the chromosome."