All of their daughters will be heterozygous #("X"^"N""X"^"n")#, so they will be carriers. Whether the grandson will or will not be colorblind depends on the genotype of the father. If he has normal color vision #("X"^"N""Y")#, the probability of their grandson being colorblind is d) nil. If the grandson's father is colorblind #("X"^"n""Y")#, then the probability of their grandson being colorblind is b) 0.5. (1/2 of the male grandchildren could be colorblind)
Both of their sons will have the dominant genotype #("X"^"N""Y")#. Whether their grandson will be colorblind depends on the genotype of the mother. If the grandson's mother is homozygous dominant #("X"^"N""X"^"N")#, then the probability of their grandson being colorblind is d) nil. If the mother is a heterozygous carrier #("X"^"N""X"^"n")#, the probability of the grandson being colorblind is b) 0.5. (1/2 of the male grandchildren could be colorblind)
