Genetics: In a certain plant, the flower petals are normally purple. Two recessi
ID: 56177 • Letter: G
Question
Genetics:
In a certain plant, the flower petals are normally purple. Two recessive mutations arise in separate plants and are found to be on different chromosomes. Mutation 1 (m1) gives blue petals when homozygous (m1/m1). Mutation 2 (m2) gives red petals when homozygous (m2/m2). Biochemists working on the synthesis of flower pigments in this species have already described the following pathway:
A) Which mutant would you expect to be deficient in enzyme A activity?
B) A plant has the genotype M1/m1 ; M2/m2. What would you expect its phenotype to be?
C) If the plant in part b is selfed, what colors of progeny would you expect and in what proportions?
D) Why are these mutants recessive?
enzyme A - > blue pigment colorless (white) compound ymeBred pigment enzyme B --> red pigmentExplanation / Answer
A. A back mutation results in the mutant that is deficient in enzyme A activity. It is also called a reversion
B. The phenotype will be colorless
C. There are three disticnt phenotypes (phenotype of homozygous recessive for both alleles is not given). The colorless:blue:red:??? are in the ratio of 0.56:0.19:0.19:0.06
D. They are recessive because a single normal gene results in white/colorless wild phenotype.
The original organim is m1m1 genotype which synthesize an enzyme responsible for breakdown of white pigment to give a blue pigment. Mutation resulted in loss of activity, and a second mutation resulted in reversion of the mutation and regained the activity of the enzyme.
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