Question

One true-breeding line of mice is obese and dark, and the other true-breeding line is lean and light. dark is dominant to light, but obese and lean exhibit incomplete dominance. the two genes involved are on separate chromosomes. what proportion of offspring from a dihybrid cross should be dark and obese?

Answer 1

Let us denote the color traits with 'D' for dark and 'd' for light. The dark color is dominant over the light color. The body weight traits, obese and lean are 'x' and 'y', respectively. Since the body weight traits show incomplete dominance over one another, they have been labelled separately. The mice with a pure line of dark-obese trait will have the 'DDoo' genotype. The mice with a pure line of light-lean trait will have the 'ddll' genotype. The resulting hybrid of the two types of mice is shown in image 1. The image 2 shows the cross between the hybrids of image 1. The proportion of offspring that will be dark and obese in the final cross between the hybrids will be, 3 (yellow) out of 16.