Question

1. In the tomato, flower color is determined by alleles of a single autosomal gene. Flowers are found in three colors: Violet, blue and white. When truebreeding violet-flowered plants are crossed with truebreeding white-flowered plants, the result is all blue-flowered plants. What would you predict to be the phenotypes among 240 progeny plants if the blue-flowered plants are crossed with violet-flowered plants?

   		60 violet, 120 blue, 60 white
   		240 violet
   		240 blue
   		120 violet, 120 blue
   		120 blue, 120 white
   		180 violet, 60 blue

Answer 1

The case provided here is an example of incomplete dominance where the violet is the dominant homozygote, blue is the heterozygote, and white is the recessive homozygote. Let the alleles be V ( for dominant, violet) and v ( for recessive)

Violet = VV, possible gametes are V

Blue= Vv, Possible gametes are V and v

White=vv, Possible gametes are v

So, now, blue-flowered plants are crossed with violet. i.e VV X Vv.

The punnet square would be

gametes	V	v
V	VV (violet)	Vv (blue)

So. out of the 240 progeny, one half would be Violet and the other half blue.

Therefore, we would expect to find 120 blue and 120 Violet flower producing plants.