In a certain dog breed, the allele B for a black coat is dominant, and the allele b for a spotted coat is recessive. What genotypes for this dog breed would lead to a spotted phenotype? **Make a punnet square for help**

Question

Responses

BB
BB

BB and bb
BB and bb

Bb
Bb

bb

Answer 1

To determine which genotypes lead to a spotted phenotype in the dog breed, we first need to clarify the dominance of the alleles:

• B (black coat) is dominant.
• b (spotted coat) is recessive.

Only the genotype bb will result in the spotted phenotype since it is the only genotype that consists solely of the recessive allele.

Let's illustrate this with a Punnett square to show the potential offspring from a cross between different genotypes:

1. Cross between two homozygous parents:

   • BB x BB
   • Gametes: B B

   |   | B | B |
   |---|---|---|
   | B | BB | BB |
   | B | BB | BB |
   

   • All offspring will be BB (black coat).

2. Cross between one homozygous dominant and one homozygous recessive:

   • BB x bb
   • Gametes: B, B and b, b

   |   | B | B |
   |---|---|---|
   | b | Bb | Bb |
   | b | Bb | Bb |
   

   • All offspring will be Bb (black coat).

3. Cross between one heterozygous and one homozygous recessive:

   • Bb x bb
   • Gametes: B, b and b, b

   |   | B | b |
   |---|---|---|
   | b | Bb | bb |
   | b | Bb | bb |
   

   • Offspring will be 50% Bb (black coat) and 50% bb (spotted coat).

4. Cross between two heterozygous parents:

   • Bb x Bb
   • Gametes: B, b and B, b

   |   | B | b |
   |---|---|---|
   | B | BB | Bb |
   | b | Bb | bb |
   

   • Offspring will be 25% BB (black coat), 50% Bb (black coat), and 25% bb (spotted coat).

From the above analyses and Punnett squares, the only genotype that leads to a spotted phenotype is:

• bb

So, the correct response to the question is bb.