Q. A man whose father was colour blind marries a woman who had a colour blind mother and normal father. What percentage of male children of this couple will be colour blind?
(a) 75%
(b) 25%
(c) 0%
(d) 50%
Solution :
Correct option : D Colour blindness in X-linked recessive disease. A man whose father was colour blind (XcY) and mother was normal (XX; we will consider normal unless mentioned otherwise), is normal (XY; as he is getting normal X from the mother and Y from the father).
Woman who had a colour blind mother (XcXc) and normal father (XY), will be the carrier (XcX; as she is getting one Xc from the mother and another X from the father).
The offspring resulting from this couple (XcX and XY are :
XcX, XcY, XX, XY.
Out of these four, 2 of them are males (XcY, XY) of which one is colour blind (XcY). So, the chances of the male child to be colourblind is 50%.
Thus, the correct answer is option (D), ‘50%’.