20. In a population of dogs, fur color is determined by two alleles: black (B) and tan (b). The black allele shows complete dominance. If a dog has tan fur, what is its genotype?
Answer: C
The genotype of a dog with tan fur is bb.
A dog with tan fur must have the genotype bb, as the tan color is expressed only when both alleles are recessive, and the black allele (B) is dominant over tan (b).
A) BB
The genotype BB represents a dog that would have black fur, as it contains two dominant alleles. Therefore, this option is incorrect for a dog with tan fur.
B) Bb
The Bb genotype indicates a dog with black fur, since the presence of one dominant allele (B) would mask the expression of the recessive tan allele (b). Hence, this option is not applicable to a dog exhibiting tan fur.
C) bb
This option is correct, as the genotype bb means the dog has two recessive alleles, resulting in the expression of tan fur. Since the presence of dominant alleles (B) would lead to black fur, only the homozygous recessive state allows for tan coloration.
D) Not enough information
This option suggests ambiguity regarding the genotype, which is incorrect. The problem provides sufficient information about the dominance of the alleles and the color phenotype to determine the genotype of a dog with tan fur.
Conclusion
The genotype bb is definitively correct for a dog with tan fur, as it is the only combination that allows for the expression of the recessive trait. All other options either represent dominant traits or do not provide enough clarity to determine the genotype accurately.