Reference no: EM1393499

Assume that two pigments, red and blue, mix to give the normal wild-type purple color of petunia petals. Separate biochemical pathways synthesize the two pigments, as shown in the top two rows of the accompanying diagram. "White" refers to compounds that are not pigments, so lack of pigment results in a white petal. Red petals would only be seen if pathway I was blocked (enzyme E), and blue petals only if pathway II was completely blocked (enzyme A). Green petals would require both blue and yellow pigment to build up in the cells. Etc. A third pathway whose compounds do not contribute pigment to petals normally does not affect the blue and red pathways, but if one of its intermediates (white3) should build up in concentration (because D is defective: dd) , it can be converted to the yellow intermediate of the red pathway. In the diagram, A to E represent enzymes; their corresponding genes, all of which are unlinked, may be symbolized by the same letters.

Pathway I ...... --> white1 -E-> blue
Pathway II ..... --> white2 -A-> yellow -B-> red
C
Pathway III ...... --> white3 -D-> white4

Assume that wild-type alleles are dominant and code for enzyme function, and that recessive alleles represent lack of enzyme function. The pathways were studied by following mutations in two genes at a time, all other genes being WT. Deduce which two gene combinations were involved to produce F2 progenies in the following ratios:

a) 9 purple: 3 green: 4 blue
b) 9 purple: 3 red: 3 blue: 1 white
c) 13 purple: 3 blue
d) 9 purple: 3 red: 3 green: 1 yellow
e) Which of the mutations is acting as a suppressor?