Genetics: In a certain plant, the flower petals are normally purple. Two recessi

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?

Explanation / 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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