In a certain plant, the flower petals are normally purple. Two recessive mutatio
ID: 63576 • Letter: I
Question
In a certain plant, the flower petals are normally purple. Two recessive mutations arise in different plant lines, and assort independently. m1/m1 plants are blue and m2/m2 plants are red. Biochemists have identified the following pathway.
Colorless precursor---->Blue pigment
Same Colorless Pre also goes to-----> Red Pigment.
Which gene encodes an enzyme that catalyzes the top pathway? Explain how you know.
Which gene encodes an enzyme that catalyzes the bottom pathway? Explain how you know.
If a double-heterozygous plant is selfed, what colors of progeny and in what proportions would you expect?
Explanation / Answer
A. M2 Gene encodes the enzyme that catalyzes the top pathway. Because in the absence of this gene, red pigment cannot be made, but blue pigment can be made.
B. M1 Gene encodes the enzyme that catalyzes the bottom pathway. Because in the absence of this gene, blue pigment cannot be made, but red pigment can be made.
C). Cross of double heterozygous plant (self) is,
M1m1M2m2* M1m1M2m2 = M1M1M2M2 (1/16, purple), M1M1M2m2 (2/16, purple), M1M1m2m2 (1/16, red), M1m1M2M2 (purple, 2/16), M1m1M2m2 (4/16, purple), M1m1m2m2 (2/16, red), m1m1 M2M2 (blue, 1/16), m11m1m2M2 (blue, 2/16), m1m1m2m2 (may be some intermediate color or white).
As mutations are recessive, presence of wild type allele always gives purple color.