If a colour blind female marries a man whose mother was also colour blind, what are the chances of her progeny having colour blindness?
- 25%
- 50%
- 75%
- 100%
Answer
(4) 100%
Solution
Colour blindness is an X-linked recessive disorder.
Colour blind female = XcXc
The man's mother was colour blind (XcXc), she must have passed Xc to her son.
The man is XcY (colour blind).
Cross: XcXc XcY
Daughters XcXc (colour blind), sons XcY (colour blind)
100% of the progeny will be colour blind.
Answer: (4)