Question

cross a colorblind female with a normal vision male. what is the phenotype ratio of the offspring?
○ 2 normal daughters: 2 colorblind sons
○ 2 colorblind daughters: 2 normal sons
○ 2 normal daughters: 2 normal sons
○ 2 colorblind daughters: 2 colorblind sons

Explanation:

Step1: Define genotypes

Colorblindness is X-linked recessive. Let $X^c$ = colorblind allele, $X^C$ = normal allele.

• Colorblind female: $X^cX^c$
• Normal male: $X^CY$

Step2: Set up Punnett square

$$\begin{array}{c|cc} & X^c & X^c \\ \hline X^C & X^CX^c & X^CX^c \\ Y & X^cY & X^cY \\ \end{array}$$

Step3: Determine phenotypes

• $X^CX^c$: Normal vision daughters (carriers)
• $X^cY$: Colorblind sons

Step4: Count phenotype ratio

2 normal daughters : 2 colorblind sons

Answer:

2 Normal Daughters: 2 Colorblind Sons