You are studying 5 genes: a, b, c, d, and e. In an attempt to map them, you perform a series of two-point crosses with the results listed below. Select the appropriate gene order based on the results of your experiment.

a-b = 15 map units;

a-c = 21 map units;

a-d = 1 map unit;

b-c = 6 map units;

b-e = 2 map units;

c-d = 20 map units;

c-e = 8 map units;

d-e = 12 map units.

Gene order will be- a,d,e,b,c

Explanation:

Gene mapping refers to the arrangement of genes on the chromosomes. The genes can be mapped on the chromosome by calculation the recombination frequency in the hybrid crosses.

The recombination frequency can be represented on the chromosomes to show the distance between the genes which is measured as centimorgan. 1 percent recombination is considered 1 cM.

In the given question, since the distance between the gene has been provided therefore the genes can be mapped on the chromosome.

This could be done in the following manner-

1. Take the highest value of distance- 21 m. u between a and c.

2. Now take c as a reference point and arrange the other distance measuring distance from the c.

3. On this basis- c-d, c-e and b-c can be plotted.

4. Now, plot other values taking an as a reference point and plot the values b-e, a-b, a-d.

5. the genes will be arranged in the order a,d,e,b,c.

Thus, a,d,e,b,c is the correct answer.

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