Genetics
Question
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The diagram below is part of a deletion mapping study on the Drosophila chromosome. These are used to characterise 6 recessive mutations on this region of the chromosome, namely a, b, c, d, e and f.
The Drosophila flies homozygous for the mutations are crossed with those homozygous for the deletions. Below is a table summarising the results for the offspring, where only offspring with a mutant phenotype are marked with an X.
What is the order of the 6 mutations, from left to right?
Alternatives
| Option | Alternative | First answers  |
Confirmed answers  |
|---|---|---|---|
| A |
b, a, d, c, e, f |
1 (14.29%) |
0 (0.00%) |
| B |
b, a, d, c, f, e |
6 (85.71%) |
2 (100.00%) |
| C |
b, a, c, d, e, f |
0 (0.00%) |
0 (0.00%) |
| D |
b, c, a, d, e, f |
0 (0.00%) |
0 (0.00%) |
| E |
b, a, c, d, f, e |
0 (0.00%) |
0 (0.00%) |
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Compare deletion 1 and 2. It is clear that b lies on both deletion 1 and 2. The locations of b and a on the chromosome are determined.
Compare deletion 3 and 5. It is clear that f lies on deletion 5 but not 3. The location of f on the chromosome is determined.
Compare deletion 4 and 6. It is clear that c lies on deletion 4 but not 6. The location of c, and consequently e, on the chromosome is determined.
Comparing the known locations of all mutations except d limits d's position to between a and c.
This thus gives the correct order b, a, d, c, f, e.