Ten individuals of two inbred strains of mice, A and B, are fed identical diets. All have normal blood sugar as adults. The same mice are then fed diets high in sugar. Mice from strain B develop diabetes, but mice from strain A do not. Diabetes in strain B mice results from:_______
a. the interaction of their diet with their genotype.
b. their genotypes, which are different from strain A mice.
c. their diets, which are different from strain A mice.
d. their norm of reaction to sugar in their diets.
e. none of these choices is correct.

Inbreeding for a long period of time is done for the purpose of comparison experiments such as this because over time, the genotypes of the offsprings become almost identical so the experiment results can be compared more easily.

In the example given in the question, both mice from strain A and strain B are fed with the same diet and mice from strain B develop diabetes whereas mice from strain A does not.

A can not be true because if the cause was solely the interaction with their genotypes, mice from strain A should have also gotten diabetes.

C can not be true because in the question, it is stated that they are fed with the same diets which can not be the cause of the different results.

Looking at option B, this result may be due to the slight difference in their genotypes even though they are inbred and most of their genotype is similar.

I hope this answer helps.