Info

Deletion 1

Chromosome

Deletion 1

Deletion 2

Deletion 3 Deletion 4

Deletion 6

Deletion 5

Deletion 1

Deletion 2

Deletion 3 Deletion 4

Deletion 6

Deletion 5

4. The locations of six deletions have been mapped to the Drosophila chromosome as shown in the following diagram. Recessive mutations a, b, c, d, e, f, and g are known to be located in the same regions as the deletions, but the order of the mutations on the chromosome is not known. When flies homozygous for the recessive mutations are crossed with flies homozygous for the deletions, the following results are obtained, where the letter "m" represents a mutant phenotype and a plus sign (+) represents the wild type. On the basis of these data, determine the relative order of the seven mutant genes on the chromosome:

Mutation b is expressed only when deletion 1 is present; so it must be located in the region of the chromosome covered by deletion 1 and none of the other deletions:

Deletion 1

Deletion 2

Deletion 3 Deletion 4

Deletion 6

Deletion 5

Using this procedure, we can map the remaining mutations. For each mutation, we look for the area of overlap among deletions that express the mutations and exclude any areas of overlap that are covered by other deletions that do not express the mutation:

Mutations

Deletion

a

b

c

d

e

f

g

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