Direction: Red-green colour blindness is inherited as a recessive X-linked trait.
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What will be the probability of having the colour-blind son to a woman with phenotypically normal parents and a colour-blind brother, and married to a normal man? (Assume that she has no previous children)
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- 100 %
- 50 %
- 25 %
- 12.5 %
Correct Option: B
The probability of having the colorblind son to woman with phenotypically normal parent and a colorblind brother, and married to a normal man than may be the woman is a carrier of blind trait or else not. Then we can say mother can be XRX a carrier or XX normal and have a cross with a normal man.
Therefore, there is 1 chance of having a colorblind son out of 4 possible progenies.
Hence, probability of one child to be colorblind = ¼ = 0.25 = 25% .
Again 2 sons could be born, out of which 1 could be colorblind;
Probability for colorblind son = ½ = 50%
