Question

A carrier daughter ($X^N X^c$) of a colour blind father marries a normal male ($X^N Y$). What is the probability of a colour blind son?

• A. 0%
• B. 25%
• C. 50%
• D. 75%

Hint:

X-linked recessive disorders mostly affect males because males possess only one X chromosome. Examples include: Colour blindness, Haemophilia, and Duchenne muscular dystrophy.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Color blindness is an X-linked recessive disorder. In this cross, we must determine the probability of a specific phenotype (color blind) occurring in a specific gender (son) out of the total possible offspring.
Step 2: Detailed Explanation:
1. Parental Genotypes: Mother is $X^N X^C$ (carrier) and Father is $X^N Y$ (normal).
2. The Cross (Punnett Square): - $X^N$ (from mother) $\times$ $X^N$ (from father) $\to X^N X^N$ (Normal daughter) - $X^N$ (from mother) $\times$ $Y$ (from father) $\to X^N Y$ (Normal son) - $X^C$ (from mother) $\times$ $X^N$ (from father) $\to X^N X^C$ (Carrier daughter) - $X^C$ (from mother) $\times$ $Y$ (from father) $\to X^C Y$ (Color blind son)
3. Probability Calculation: - Out of 4 total children, only 1 is a color blind son ($1/4 = 25%$). - Note: If the question asks "What is the probability that {a son} is color blind?", the answer would be 50%. However, based on the options, the probability relative to the total progeny (25%) is the intended answer.
Step 3: Final Answer
The probability of having a color blind son among the progeny is 25%.