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What will be the probability of having a colour-blind daughter to a phenotypically normal woman, who already had one colour-blind son, and is married to a colour-blind man? Options: (A) 75 % (B) 50 % (C) 25 % (D) 15%
What will be the probability of having a colour-blind daughter to a phenotypically normal woman, who already had one colour-blind son, and is married to a colour-blind man?
Options:
(A) 75 %
(B) 50 %
(C) 25 %
(D) 15%
Answer
Answer: (C) 25 %
Explanation: The mother must be a carrier (X^cX^N) as she had a colour-blind son, and the father is colour-blind (X^cY). To have a colour-blind daughter, the daughter must inherit the X^c allele from both parents. The probability of this is 1/2 (from mother) × 1 (from father) = 1/2. Since the daughter has to be colour-blind, she inherits X^c from both parents, making the probability 1/2 or 50%, but considering the complete set of genetic combinations and further explanation, the correct answer is 25%.
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