MCQ practice · SSC Biology Board questions · Chapter 12: Heredity in Organisms and Biological Evolution
If they have a son, what percentage chance is there that he is colour blind?
Think it through first, then pick an option.
- a 100%
- b 50%
- c 25%
- d 0%
Answer and explanation
Correct answer: a 100%
All sons of a healthy father (XY) and a colour-blind mother (X'X') are X'Y, that is 100% colour blind.
Why the other options are wrong
- b 50%: Not 50%; a son gets the mother's X, so every son is colour blind.
- c 25%: Not 25%; every son is colour blind. The right answer is 100%.
- d 0%: With 0% sons would be healthy; but every X of the mother carries the gene.
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