Final answer:
In mouse genetics, a homozygous brown mouse (BB) crossed with a homozygous white mouse (bb) produces offspring with a genotypic ratio of 100% Bb and a phenotypic ratio of 100% brown fur.
Step-by-step explanation:
In mouse genetics, fur color is often used as an example to illustrate basic inheritance patterns, including dominance, recessiveness, and more complex interactions such as epistasis. When considering the cross between a homozygous brown mouse and a homozygous white mouse, one must first determine the genotype of each parent to predict the genotypic and phenotypic ratios of their offspring.
A homozygous brown mouse would have a genotype of BB (if we assume the information provided meant B for brown and not b, as typically brown is denoted by a 'B'), and a homozygous white mouse would have the genotype bb. When these two mice mate, each parent can only pass on one allele for the fur color gene to their offspring. Therefore, all offspring from this cross would be heterozygous Bb, having brown fur since the B allele is dominant.
Genotypically, the ratio would be 100% Bb. Phenotypically, 100% of the offspring would have brown fur. It's important also to understand that separate genes could interact to affect the phenotype through epistasis. In such a case, a gene at another locus could entirely mask the expression of the fur color genes we just discussed, but this aspect was not directly relevant to the original question posed by the student.