Assumptions:
* Simple Inheritance: We're assuming that coat color is determined by a single gene with two alleles, one for brown (let's say "B") and one for white ("b").
* Dominant Allele: Brown is dominant, meaning a mouse with at least one "B" allele will have brown fur.
Solving the Problem
1. Parental Generation (P): A brown mouse (BB or Bb) is mated with a white mouse (bb).
2. First Filial Generation (F1):
* Since the white mouse can only contribute a "b" allele, all F1 offspring will inherit at least one "B" allele.
* This means all F1 offspring will be brown (Bb).
3. Second Filial Generation (F2):
* When two F1 mice (Bb) mate, there are four possible combinations of alleles:
* BB (brown)
* Bb (brown)
* Bb (brown)
* bb (white)
4. Fraction of Brown Mice:
* Out of these four possibilities, three result in a brown mouse (BB, Bb, Bb).
* Therefore, 3/4 of the F2 mice will be brown.
Answer: 3/4 (or 75%) of the F2 mice will be brown.