94. The following figure depicts the relationship between a genetic map for four genes (A, B, C and D) and their corresponding physical map.

The following statements are made to explain this relationship.
A. More number of recombination events occur between A and B as compared to B and C.
B. Lesser number of recombination events occur between C and D as compared to B and C.
C. Although the physical distance between A and B is less than that between C and D, the region between A and B is more recombinogenic.
D. The physical distance between A and B is less than that between C and D, and thus the region between A and B is less recombinogenic.
E. Although the physical distance between C and D is more than that between B and C, the region between C and D is less recombinogenic.
F. Although the physical distance between C and D is more than B and C. the region between C and D is more recombinogenic.
Which statements are correct?
(1) A and B       (2) C and E
(3) D and F      (4) A, C and E

A and B are located in a smaller physical interval but show the same genetic distance as B–C and C–D; therefore, the correct statements are C and E, so the right option is (2).​

Introduction

In gene mapping, the genetic map (in cM) reflects recombination frequency, while the physical map (in kb or Mb) shows actual DNA length, and the two are often non‑linear because of recombination hotspots and cold spots. This CSIR NET Life Science question compares four genes (A, B, C, D) with equal genetic distances but unequal physical distances to test understanding of recombinogenic regions.​

Understanding the map in the question

• Genetic map: A–B = 10 cM, B–C = 10 cM, C–D = 10 cM.

• Physical map: A–B = 8 kb, B–C = 10 kb, C–D = 14 kb.

Equal genetic distances mean the average recombination frequency is the same in all three intervals, but unequal physical distances mean the recombination rate per kilobase is different. A short physical interval with the same genetic distance must be more recombinogenic (more crossovers per kb), whereas a longer physical interval with the same genetic distance must be less recombinogenic.​

Option‑wise explanation

Option A

“More number of recombination events occur between A and B as compared to B and C.”

A–B and B–C are both 10 cM genetically, so the number (frequency) of recombination events per meiosis between A–B and B–C is equal, not more in A–B. Thus, statement A is incorrect.​

Option B

“Lesser number of recombination events occur between C and D as compared to B and C.”

Again, C–D and B–C are both 10 cM; the recombination frequency is the same, so the number of recombination events is not lesser between C–D. Therefore, statement B is incorrect.​

Option C

“Although the physical distance between A and B is less than that between C and D, the region between A and B is more recombinogenic.”

• Physical distances: A–B = 8 kb; C–D = 14 kb (A–B is shorter).

• Genetic distances are equal (10 cM each), so crossovers per kb must be higher in the shorter interval.​

Hence, the A–B region has more recombination per unit length (is more recombinogenic), making statement C correct.

Option D

“The physical distance between A and B is less than that between C and D, and thus the region between A and B is less recombinogenic.”

This reverses the correct reasoning: a shorter physical interval with the same cM must be more, not less, recombinogenic. Therefore, statement D is incorrect.​

Option E

“Although the physical distance between C and D is more than that between B and C, the region between C and D is less recombinogenic.”

• Physical distances: B–C = 10 kb; C–D = 14 kb (C–D is longer).

• Genetic distances: both 10 cM, so recombination frequency per meiosis is equal.

Because C–D covers more kb for the same 10 cM, its recombination rate per kb is lower, so it is less recombinogenic than B–C. Thus, statement E is correct.​

Option F

“Although the physical distance between C and D is more than B and C, the region between C and D is more recombinogenic.”

As argued above, a longer physical interval with the same genetic distance must have fewer crossovers per kb, so it cannot be more recombinogenic. Hence, statement F is incorrect.​

Final answer

The correct statements are C and E, hence the correct option is (2) C and E.