Principle of Inheritance and VariationEasyBloom L3
Question
Red-green colour blindness is a human recessive sex-linked trait. A man and a woman with normal vision have a colour-blind son. What is the probability that their next child will also be a color-blind son?
Options
A.0
B.1/8
C.1/4
D.1/2
Solution
Sol.(c) [Key Concept: X-linked Colour Blindness — Probability Calculation] Since they have a colour-blind son, the mother must be a carrier (X^C X^c). Cross: X^C X^c × X^C Y → sons: 1/2 normal (X^C Y) + 1/2 colour blind (X^c Y); daughters: 1/2 normal (X^C X^C) + 1/2 carrier (X^C X^c). Probability of next child being male = 1/2; probability of colour blind given male = 1/2. Probability of colour-blind son = 1/2 × 1/2 = 1/4.
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