Question

A man whose father is a colour blind, marries a woman, who is a daughter of a colourblind mother. The offsprings of this couple will be
A. All daughter and sons are colourblind,
B. 50% colourblind and 50% normal sons
C. Carrier normal son and color blind daughter
D. Colourblind sons and normal daughters.

Answer 1

Colour blindness is a usually a genetic (hereditary) X linked recessive condition. Red/green and blue colour blindness is usually passed down from your parents. The gene which is responsible for the condition is carried on the X chromosome and this is the reason why many more men are affected than women.

Complete step by step answer:
As color blindness is an autosomal recessive genetic disorder, for it is present at X -chromosome. Thus, as we see the situation given in the question, a man whose father was color blind (will be, i.e, XY normal) marries a woman whose mother was color blind (i.e, this woman will be a carrier $\left( {{X_C}X} \right)$ So, a man whose father was colour blind mother considered being normal means FATHER $\left( {{X_C}Y} \right)$ MOTHER (XX) so father give Y and mother give X to the son(XY), so the son will be normal and the women who is a daughter of colorblind mother, so father will be considered normal so FATHER $\left( {{X_C}Y} \right)$ MOTHER $\left( {{X_C}{X_C}} \right)$ so father give X and mother give ${X_C}$ to their daughter $\left( {{X_C}X} \right)$
So SON (XY) DAUGHTER $\left( {{X_C}X} \right)$
Thus, when marriage will happen between a normal man and a carrier woman,
their offsprings SONS (XY) $\left( {{X_C}Y} \right)$ DAUGHTERS$\left( {X{X_C}} \right)$ (XX)
in that case, the percentage of a male child to be colorblind is 50% from the sons
So the correct option is B

Note: 99% of all colorblind people are suffering from red-green color blindness. When using color correcting lenses you are wearing two different colored lenses in your eyes. Red-green color blindness is a recessive sex-linked trait, which causes more men to be colorblind than women.