, 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.