Question

For dogs, a black coat color (B) is dominant over a brown coat (b). Imagine that a dog with a black coat is mated with a dog with a brown coat. If each of their litters includes some puppies that are brown and others that are black, what can be concluded about the parents?

1) The black dog must be heterozygous for the B allele.
2) The black dog must be homozygous for the B allele.
3) The brown dog must be heterozygous for the B allele.
4) They are true breeding.

Answer 1

If a black-coated dog is mated with a brown-coated dog and their litters include both black and brown puppies, it can be concluded that the black-coated dog must be heterozygous for the B allele.

Step-by-step explanation:

In this case, if a black-coated dog (B) is mated with a brown-coated dog (b) and their litters include both black and brown puppies, it can be concluded that the black-coated dog must be heterozygous for the B allele. This means that the black-coated dog has one dominant B allele and one recessive b allele.

When the black-coated dog and brown-coated dog are mated, there is a 50% chance that the black-coated dog passes on the dominant B allele, resulting in black puppies. There is also a 50% chance that the black-coated dog passes on the recessive b allele, resulting in brown puppies.

Therefore, the correct conclusion is that the black dog must be heterozygous for the B allele (option 1).