Question

Given diagram shows a pair of homologous chromosomes during meiosis. Maximum crossing over will occur between genes

• A. A and a; D and d
• B. C and d; c and D
• C. B and c; b and C
• D. A and a; d and D

Hint:

1% Recombination Frequency = 1 Map Unit (Centimorgan). Genes further apart have higher map units.

Answer 1

The Correct Option is D

Step 1: Principle of Crossing Over:
The frequency of crossing over between two genes on the same chromosome is directly proportional to the physical distance between them. \[ \text{Crossing Over Frequency} \propto \text{Distance between genes} \]
Step 2: Analyzing the Diagram:
The genes are arranged linearly as A-B-C-D.

• Genes A and D are located at the extreme ends of the chromosome.
• Genes B and C are in the middle.

The distance between A and D is the maximum.
Step 3: Conclusion:
Since the distance is maximum between loci A and D, the probability of a crossover event occurring in the region between them is the highest. Thus, maximum crossing over (recombination) occurs between the genes A/a and D/d.
Step 4: Final Answer:
Option (D) represents the gene pairs at the ends.