Question

In a certain species of plant, flowers occur in three colors: blue, pink, and white. A pure-breeding pink plant is mated with a pure-breeding white plant. All of the F1 are blue. When the blue F1 plants are selfed, the F2 occurs in the ratio 9 blue:3 pink:4 whitE. How many gene pairs control the flower color phenotype?

Answer 1

Answer: If the F2 occurs in the ratio 9 blue:3 pink:4 white, one gene pair (i.e 2 genes) control the flower color phenotype.

Explanation: This principle is called INCOMPLETE DOMINANCE where one gene (dominant) won't completely override the other (recessive).

Let assume B represents the dominant gene and b represents the reccesive gene. Let also assume that Blue color is dominant over white color. We can assign the genotype as follows;

Homozygous dominant genes BB will produce Blue color

Homozygous recessive genes bb will produce white color

Heterozygous genes Bb will produce pink color.

Therefore, a pair of gene ( 2 genes) will determine the flower color phenotype.