Question

• dihybrid cross problems

1. in horses, the coat color black is dominant (b) over chestnut (b). the trotting gait is dominant (t) over the pacing gait (t). if a homozygous black pacer is mated to a homozygous chestnut, heterozygous trotter, what will be the probabilities for genotype and phenotype of the f₁ generation?

parent 1: bbtt
parent 2: bbtt

Explanation:

Step1: Identify parent gametes

Parent 1 ($BBtt$) gametes: $Bt$
Parent 2 ($bbTt$) gametes: $bT, bt$

Step2: Set up Punnett square

$$\begin{array}{c|cc} & Bt \\ \hline bT & BbTt \\ bt & Bbtt \\ \end{array}$$

Step3: Calculate genotype probabilities

• $BbTt$: $\frac{1}{2} = 50\%$
• $Bbtt$: $\frac{1}{2} = 50\%$

Step4: Map to phenotypes

• $BbTt$: Black (B dominant) + Trotter (T dominant) → 50%
• $Bbtt$: Black (B dominant) + Pacer (t recessive) → 50%

Answer:

Genotype Probabilities:

1. $BbTt$: 50%
2. $Bbtt$: 50%

Phenotype Probabilities:

1. Black trotter: 50%
2. Black pacer: 50%