Cell differentiation depends on changes in expression.

it depends on changes in gene expression

#1. 25 percent of the offspring would be white

Explanation

heterozygous means that both the parents genotype would be Bb. If you make a Punnett square out of this you end up with 75 percent brown gerbils and 25 percent white because if the B gene is present at all the gerbil will be brown and only 1/4 combinations is bb.

#2. 75

Explanation

We already know from the previous question that 25% of the offspring will be white. For this question we just have to take 25% of three hundred. So multiply 300 time 0.25 which equals 75.