Two New Mutant Lines of a Flowering Plant Have Been $\times$

question 47

Multiple Choice

Two new mutant lines of a flowering plant have been obtained; one breeds true for blue flower color and the other breeds true for red flower color (wild-type flower color is purple) . Consider the following crosses.
1. blue $\times$ purple $\rightarrow F _ { 1 }$ all purple $\rightarrow F _ { 2 } 75 \%$ purple; $25 \%$ blue
2. red $\times$ purple $\rightarrow \mathrm { F } _ { 1 }$ all purple $\rightarrow \mathrm { F } _ { 2 } 75 \%$ purple; $25 \%$ red
3. red $\times$ blue $\rightarrow F _ { 1 }$ all purple

If the red pigment is a precursor of the purple pigment,the blue pigment is a precursor of the red pigment,and a colorless compound is the precursor of the blue pigment in a linear biosynthetic pathway controlling flower color,what phenotypic ratios do you expect in the F₂ of cross 3?

• A)3 purple : 1 white (colorless)
• B)9 purple : 3 blue : 3 red : 1 white (colorless)
• C)9 purple : 4 blue : 3 red
• D)9 purple : 7 white (colorless)
• E)12 purple : 3 blue : 1 white (colorless)