Question

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?

Answer 1

Among these three, compounds A is lethal to organism. It has to convert to blue or red. Compound A(green) is converted to compound B(blue) by gene A. So a function gene with AA, or AA is required. genotype with aa is lethal to organism.

SELF CROSS:

Parents AaBb X AaBb

Gamets AB Ab aB ab AB Ab aB ab

male/ female	AB	Ab	aB	ab
AB	AABB	AABb	AaBB	AaBb
Ab	AABb	AAbb	AaBb	Aabb
aB	AaBB	AaBb	aaBB	aaBb
ab	AaBb	Aabb	aaBb	aabb

1. From the the above progeny aaBB, aaBb and aabb are dead organism, becuase they lack function gene A

2. AABB, AABb, AaBB and AaBb these organisms contain functional copy of Gene B and will convert compount B(Blue) into compound C (red).

3. AAbb and Aabb these organisms contain functional copy of Gene A and will convert compound A(green) into compoind B(blue).

4. From the above observation there are 9 organisms that are Red (able to convert blue to red)

3 organisms that are Blue (able to convert green to blue)