Question

Determine the order of genes along a chromosome based on the following recombination frequencies : A-B, 8 map units; A-C, 28 map units; A-D, 25 map units; B-C, 20 map units; B-D, 33 map units:

Options

• A-C-D-B

• C-D-B-A

• D-A-B-C

• B-A-C-D

Answer 1

D-A-B-C

Explanation:

The map units represent the distances between genes, with one map unit roughly equivalent to 1% recombination frequency. The smallest distance is between A and B (8 units), so these two are close together. Distances A-D (25 units) and A-C (28 units) suggest that D and C are farther apart from A. Considering the distances between B-C (20 units) and B-D (33 units), the order placing D near A and B, followed by C farthest, fits best. This arrangement respects the given recombination frequencies and the principle that recombination frequencies correspond to linear distances on a chromosome. Thus, the gene order is D-A-B-C.