Question

Assume that two pigments, red and blue, mix to give the normal purple color of petunia petals. Separate biochemical pathways synthesize the two pigments, as shown in the top rows of the accompanying diagram. "White" refers to compounds that are not pigments. Total lack of pigment results in a white petal. Red pigment forms from a yellow intermediate that is normally at a concentration too low to color petals. A third pathway, whose compounds do not contribute pigments to petals, normally does not affect the red and blue pathways, but, if one of its intermediates (white3) should build up in concentration, it can be converted into the yellow intermediate of the red pathway. pathway I ... -> white1 --E--> blue pathway II ... -> white2 --A--> yellow --B--> red ^ | C | pathway III ... -> white3 --D--> white4 In the diagram, the letters A through E represent enzymes; heir corresponding genes, all of which are unlinked, may be symbolized by the same letters. Assume that wild-type alleles are dominant and encode enzyme function and that recessive alleles result in a lack of enzyme activity. Deduce which combinations of true-breeding parental genotypes could be crossed to produce F2 progeny in the following ratios. Assume no mutations are lethal; also, blue mixed with yellow produces green. 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

Assume that two pigments, red and blue, mix to give the normal purple color of petunia petals. Separate biochemical pathways synthesize the two pigments, as shown in the top rows of the accompanying diagram. "White" refers to compounds that are not pigments. Total lack of pigment results in a white petal. Red pigment forms from a yellow intermediate that is normally at a concentration too low to color petals. A third pathway, whose compounds do not contribute pigments to petals, normally does not affect the red and blue pathways, but, if one of its intermediates (white3) should build up in concentration, it can be converted into the yellow intermediate of the red pathway.

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

In the diagram, the letters A through E represent enzymes; heir corresponding genes, all of which are unlinked, may be symbolized by the same letters.

Assume that wild-type alleles are dominant and encode enzyme function and that recessive alleles result in a lack of enzyme activity. Deduce which combinations of true-breeding parental genotypes could be crossed to produce F2 progeny in the following ratios. Assume no mutations are lethal; also, blue mixed with yellow produces green.
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

Assume that two pigments, red and blue, mix to give the normal purple color of petunia petals. Separate biochemical pathways synthesize the two pigments, as shown in the top rows of the accompanying diagram. "White" refers to compounds that are not pigments. Total lack of pigment results in a white petal. Red pigment forms from a yellow intermediate that is normally at a concentration too low to color petals. A third pathway, whose compounds do not contribute pigments to petals, normally does not affect the red and blue pathways, but, if one of its intermediates (white3) should build up in concentration, it can be converted into the yellow intermediate of the red pathway.

pathway I ... -> white1 –E–> blue
pathway II ... -> white2 –A–> yellow –B–> red
^
|
C
|
pathway III ... -> white3 –D–> white4

In the diagram, the letters A through E represent enzymes; heir corresponding genes, all of which are unlinked, may be symbolized by the same letters.

Assume that wild-type alleles are dominant and encode enzyme function and that recessive alleles result in a lack of enzyme activity. Deduce which combinations of true-breeding parental genotypes could be crossed to produce F2 progeny in the following ratios. Assume no mutations are lethal; also, blue mixed with yellow produces green.
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

Added by Troy C.

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