Question

If a colour-blind female marries a man whose mother was also colour blind, what are the chances of her progeny having colour blindness?

• A. 100%
• B. 25%
• C. 50%
• D. 75%

Hint:

In X-linked recessive inheritance, if the mother is affected, all her sons will definitely be affected. If both the mother and father are affected, all offspring, regardless of gender, will be affected.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Color blindness is an X-linked recessive trait. This means males only need one affected X chromosome (\(X^c Y\)) to show the trait, while females need two (\(X^c X^c\)).
Step 2: Key Formula or Approach:
Identify the genotypes of the parents and perform a Punnett square cross.
Step 3: Detailed Explanation:
1. Female Genotype: She is color-blind, so she must be \(X^c X^c\). 2. Male Genotype: The man's mother was color-blind (\(X^c X^c\)). Since a son always inherits his X chromosome from his mother, he must have received the \(X^c\) allele. Therefore, the man is \(X^c Y\) (color-blind). 3. The Cross: \(X^c X^c\) (Female) \(\times\) \(X^c Y\) (Male). 4. Progeny Analysis: - All daughters will receive \(X^c\) from mother and \(X^c\) from father \(\to X^c X^c\) (Color-blind). - All sons will receive \(X^c\) from mother and \(Y\) from father \(\to X^c Y\) (Color-blind). 5. All children (100%) will be color-blind.
Step 4: Final Answer
The chances of the progeny having color blindness are 100%.