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 2

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?

Accepted Answer

, Alfred Sturtevant used the frequency of recombination between gene pairs as a measure of the distance between genes to map their position on the chromosome . The recombination frequency (%) is proportional to the map distance.

To solve:
1.  Identify the longest distance to find the outer genes: a & d = 29%. So, the sequence spans from a to d.
2.  Place intermediate genes based on distances:
    *   a - b = 20% and b - d = 9%. Sum: 20 + 9 = 29. So, b is between a and d.
    *   a - c = 5% and c - d = 24%. Sum: 5 + 24 = 29. So, c is between a and d.
3.  Determine relative order of c and b:
    *   We know a - c = 5%.
    *   We know a - b = 20%.
    *   Therefore, c is closer to a than b is. The order from a is a - c - b.
4.  Verify with remaining data:
    *   Distance c - b should be . (Matches given data: b & c = 15%).
    *   Distance c - d should be . (Matches given data: c & d = 24%).

Conclusion: The sequence is a - c - b - d.

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