The correct option is A The males containing the single affected X chromosome are colour blind.
Human males are heterozygous, since they carry sex chromosomes as XY. But the Y chromosome cannot carry any gene. Only X chromosome can carry genes. Thus, if defective gene for colour blindness resides on X chromosome, the male offspring will become colourblind. Whereas, human females can survive as carrier for colour blindness, that it XC Xc. Only when females have Xc Xc the female offspring will have the disease.