In the DetBrisk plant the synthesis of aqua pigment in the p

In the DetBrisk plant, the synthesis of aqua pigment in the petals is controlled by two genes, B and Q; the WT allele is dominant for both genes. (Unless told otherwise, you can always assume all other genes in a pathway are homozygous WT in these individuals.) The pathway is…

a) If a pure breeding plant was unable to catalyze the first reaction, what color of petals would you expect to see?

b) If a pure breeding plant was unable to catalyze the second reaction, what color of petals would you expect to see?

c) If the pants from parts a and b were crossed, what color petals will the F1 plants have?

d) What would be the expected phenotypic ratios in a cross between F1 plants? Make sure you include phenotypic class information with your ratios.

pink pigment gene B enzyme gene Q blue enzyme aqua pigment pigment

Solution

Answer:

a. If enzyme B is missing, a pink intermediate will accumulate and the petals will be pink.

b. If enzyme Q is missing, a blue intermediate will accumulate and the petals will be blue.

c. Parents: b/b ; Q/Q * B/B ; q/q

F1: B/b ; Q/q (Aqua)

d. Parents: b/b ; Q/Q * B/B ; q/q

F1: B/b ; Q/q * B/b ; Q/q

F2: 9 B/– ; Q/– (Aqua)

3 b/b ; Q/– (Pink)

3 B/– ; q/q (Blue )

1 b/b ; q/q (Pink)

The ratio of Aqua : Blue : Pink would be 9:3:4.