Analyze the information given for each of the following Drosphila mutations, sta

Question

Analyze the information given for each of the following Drosphila mutations, state whether each is most likely a loss-of-function or a gain-of-function mutation, and explain why.

a) Flies homozygous for the recessive allele vermillion (v) have bright red eyes instead of the darker deep-red color seen in animals with the wild-type (V) allele. Homozygous vv flies lack tryptophan 2,3-dioxygenase, an enzyme used in eye-pigment biosynthesis. A distinct mutation del(v) deletes the v gene. When the phenotypes of three types of heterozygotes, Vv, del(v) V, and del(v) v, are compared, Vv and del(v) V animals have normal-colored eyes just like VV animals, but del(v) v have bright-red eyes just like vv animals.

b) The dominant allele Lobe (L) results in small, kidney-bean-shaped eyes. Wild-type animals (ll) have oval-shaped eyes. Homozygotes for the L allele die. A distinct mutation del(L) deletes the L gene. When the phenotypes of two types of heterozygotes, Ll and del(L) l, are compared, Ll animals have the Lobe phenotype, but del(L) l have normal eyes.

c) The dominant allele Notch (N) results in wings that have notches along their edges instead of the normal smooth shape (n). Homozygotes for the N allele die. A distinct mutation del(N) deletes the N gene. When the phenotypes of two types of heterozygotes, Nn and del(N) n, are compared, both have identical, mutant phenotypes.

Explanation / Answer

a) loss of function. Having one copy of the recessive allele does not affect the mutant phenotype. b) gain of function. not having a copy of the dominant allele in the heterozygote changes the phenotype from mutant Lobe to normal. c) loss of function. not having a copy of the dominant allele in the heterozygote does not change the mutant phenotype.

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