Question

using the same information from the previous three questions, cross a heterozygous running, heterozygous black mouse with a heterozygous running, heterozygous black mouse. what is the phenotype ratio of the offspring?
○ 9 running black: 3 running brown: 3 waltzing black: 1 waltzing brown
○ 8 running black: 8 waltzing brown
○ 16 running black
○ 10 running black: 3 running brown: 2 waltzing black: 1 waltzing brown

Explanation:

Step1: Define allele symbols

Let \(R\) = dominant running allele, \(r\) = recessive waltzing allele; \(B\) = dominant black allele, \(b\) = recessive brown allele. Parent genotypes: \(RrBb \times RrBb\)

Step2: Split into monohybrid crosses

For running/waltzing: \(Rr \times Rr\) gives phenotype ratio \(3\) running : \(1\) waltzing.
For coat color: \(Bb \times Bb\) gives phenotype ratio \(3\) black : \(1\) brown.

Step3: Combine ratios using product rule

• Running Black: \(3 \times 3 = 9\)
• Running Brown: \(3 \times 1 = 3\)
• Waltzing Black: \(1 \times 3 = 3\)
• Waltzing Brown: \(1 \times 1 = 1\)

Answer:

9 Running Black: 3 Running Brown: 3 Waltzing Black: 1 Waltzing Brown