Principles of Inheritance and Variation Question 174

174. A normal woman, whose father was colourblind is married to a normal man. The sons would be

[2004]

(a) $75 \%$ colour-blind

(b) $50 \%$ color-blind

(c) all normal

(d) all colour-blind

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Answer : b

Hints & Solution

(b) Normal woman with colour blind father would be a carrier.

Woman $(\mathbf{X}^{c} \mathbf{X})$ $X$ Normal man (XY)
Progeny $\underset{\substack{\text{ normal } \\ \text{ but carrier } \\ \text{ daughter }}}{X^{c} X}$ $\underset{\substack{\text{ normal } \\ \text{ daughter }}}{XX}$ $\underset{\substack{\text{ colour blind } \\ \text{ son }}}{X^{C} Y}$ $\underset{\substack{\text{ normal } \\ \text{ son }}}{X Y}$

$50 \%$ of the sons would be colour blind.



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