Question

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?

1) 25%
2) 0%
3) 50%
4) 75%

Answer with explaination please.

Answer 1

25 per cent......
......

Answer 2

the gene for colour blindness is located on the X chromosome...

the man had colour blind father which means that he would be normal as this is the case of criss cross inheritance. the man would not get the gene of colourblindness from his father ...so his genotype would be XY.

The woman had a colourblind  mother ....according to criss cross inheritance she would be the carrier of the disease...her genotype would be XXc.

we have the genotypes of both parents..

                       XY                   x            XXc

gametes:     X        Y                       X                 Xc

   

   F1 prgeny          XX         XXc            XY            XcY

                         (normal)    (normal)    (normal)      (affected)

so we can see that 25% (1/4)  of the progeny is  colour blind.....

i hope u get that right...........