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 cross between a double heterozygote and an all recessive individual, what proportion of green to red offspring should be seen?

The options

a. 3:4

b. 3:1

c. 4:3

d. 4:9

e. 1:3

The CORRECT ANSWER IS e.

e. 1:3

Explanation:

Compound A (green) , GENE A is transformed to Compound B (blue)

Compound B (blue) , GENE B is transformed to Compound C (red)

After gene A as transformed the compund A to compound B, gene B can can transform the compound B to C. Therefore, once gene A is forming blue colour from green, gene B as the capability to form red colour from the blue one.

Lets cross AaBb X AaBb (the product of the cross is shown in the attached image. )

we will have the following genotypes:

AABB-1

AABb- 2

AaBB-2

AaBb-4

We obtain a functional copy of A and B gene from the cross. Thus, the transformation of colour will proceed from green to red and they will form red colour, giving us 9 red colour.

AA bb -1

Aa bb -2

The functional B gene is absent in these organism while the funtional A gene can be seen, thus only blue colour will be formed or 3 individual will give the blue colour.

aa BB -1

aa Bb -2

aa bb-1

these set of individual will not give or form any colour as they do not possess the functional A gene which is a requirement for starting the cascade of transforming the compounds.

Therefore, the blue to red offspring will be

3:9 or 1:3

The CORRECT ANSWER is e.