To determine the possible hair color and allele combinations for the other parent based on the given information, we can analyze the genetics involved:
- Blonde hair (b) is recessive.
- Brown hair (B) is dominant.
The first parent has the genotype Bb (brown hair), which means they carry one dominant allele (B) for brown hair and one recessive allele (b) for blonde hair.
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First Child (bb): The first child has blonde hair, meaning they must have the genotype bb. For the child to have this genotype, they must have inherited a recessive allele (b) from both parents. Therefore, the other parent must also have contributed a recessive allele (b).
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Second Child (BB): The second child has brown hair and a genotype of BB. This indicates that they have received a dominant allele (B) from both parents. Since the first parent is Bb, they can contribute either a B or a b allele. However, to produce a child with the BB genotype, the other parent must have at least one dominant allele (B) to contribute.
Given these observations:
- The first child (bb) tells us the other parent has to have at least one recessive allele (b), so this parent must have a genotype of either Bb (heterozygous) or bb (homozygous recessive).
- The second child (BB) indicates the other parent must have the dominant allele (B), making it impossible for the other parent to be bb.
Conclusion: The other parent's genotype must be Bb (they have brown hair but also carry the recessive blonde allele).
So, the other parent's hair color and allele combination is:
- Hair Color: Brown
- Genotype: Bb