Question

Girl of normal vision whose father was colorblind marries a man of normal vision whose father was also colourblind. The sons of this marriage would be

• A. All normal visioned
• B. All colourblind
• C. \(50\%\) colourblind
• D. \(25\%\) colourblind

Hint:

The girl must be a carrier because she got the defective X from her colour-blind father.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
Colour blindness is an X-linked recessive trait. Let the normal allele be \(X\) and the defective allele be \(X^{c}\).

Step 2: Find the parents
The girl has normal vision but her father was colour-blind (\(X^{c}Y\)), so she received \(X^{c}\) from him and is \(XX^{c}\), a carrier.
The husband has normal vision, so he is \(XY\).

Step 3: The cross
\(XX^{c} \times XY\) gives daughters \(XX\) and \(XX^{c}\), and sons \(XY\) and \(X^{c}Y\).

Step 4: Sons
Sons get their X only from the mother, so half the sons get \(X^{c}\) and are colour-blind, which is \(50\%\).

Final Answer:
Half of the sons, that is \(50\%\), will be colour-blind. \[ \boxed{\text{(C) }50\%\ \text{colourblind}} \]