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, so the colour blind female is XcXc.
The man's mother was colour blind (XcXc), she must have passed Xc to her son, so the man is XcY (colour blind).
In the cross XcXc XcY, all daughters are XcXc (colour blind) and all sons are XcY (colour blind).
100% of the progeny will be colour blind.
Answer: (4)