A white mouse has parents that are both white. The white mouse produces only brown offspring when it mates with a brown mouse. What genotype is the white mouse?
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4 points
homozygous dominant
insufficient information to determine genotype
heterozygous
homozygous recessive
From the given information, we know that the white mouse only produces brown offspring when it mates with a brown mouse. This means that the white mouse must carry the gene for brown fur, even though it does not express it.
If the white mouse had a genotype of homozygous dominant (BB), it would only produce offspring with brown fur. However, since it can produce white offspring when mating with another white mouse, it cannot have a genotype of homozygous dominant.
If the white mouse had a genotype of heterozygous (Bb), it would carry one gene for white fur and one gene for brown fur. This would explain why all of its offspring with a brown mouse have brown fur, as the brown fur gene is dominant over the white fur gene.
If the white mouse had a genotype of homozygous recessive (bb), it would only have the gene for white fur. In this case, it would not be possible for it to produce brown offspring when mating with a brown mouse, so this genotype can be ruled out.
Therefore, the genotype of the white mouse is most likely heterozygous (Bb).