Gene A converts compound A green to compound B blue Gene B c

Gene A converts compound A (green) to compound B (blue). Gene B converts compound B to compound C (red). These compounds determine the color of the individual. In a self cross of AaBb individuals, what proportion of blue to green offspring should be seen?

I know I have seen this question posted here in a variety of forms but what is particularly troubling to me about this question is:

1. How exactly should I approach this question?

2. How can there be ANY green individuals if gene A converts green to blue?

3. How is there a complete lack of red individuals if Gene B converts blue to green

Solution

Answer:

1. How exactly should I approach this question?

AaBb x AaBb

Presence of both dominant A and B = Red

Presence of A and b = Blue

Presence of a and B = Green

AB

Ab

aB

ab

AB

AABB (red)

AABb (red)

AaBB (red)

AaBb (red)

Ab

AABb (red)

AAbb (Blue)

AaBb (red)

Aabb (Blue)

aB

AaBB (red)

AaBb (red)

aaBB (green)

aaBb (green)

ab

AaBb (red)

Aabb (Blue)

aaBb (green)

aabb (green)

3 blue: 4 green

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