Question

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?

• A. a, d, b, c
• B. d, b, a, c
• C. a, b, c, d
• D. a, c, b, d

Answer 1

The Correct Option is D

To determine the sequence of these genes on a linear chromosome, we use the given recombination frequencies, which are directly related to the physical distances between genes on the chromosome. Genes that are closer together on a chromosome have lower recombination frequencies, while genes further apart have higher frequencies. We'll follow these steps:

1. Start by identifying the pair with the smallest recombination frequency, as they are closest together: Genes a & c have a recombination frequency of 5%.
2. Next, we examine the recombination frequencies between the other genes and compare them to this initial pair to ascertain their positions:
   • The recombination frequency between b & c is 15%. Given that a & c are 5% apart, b should be placed further from c than a.
   • The recombination frequency between a & b is 20%. This suggests b is further from a, which confirms that b is between a & d. Hence, b should be placed beyond c from a.
   • The recombination frequency between c & d is 24%. This indicates that d is placed furthest from c compared to a, b, and c.
3. From the above observations, the order of the genes starting from a is in line with these rates: a, c, b, d.

Thus, the correct sequence of the genes is a, c, b, d.