If a color-blind (x-linked recessive trait) man marries a woman who is heterozygous for the trait, what proportion of their male offspring can be expected to be color blind?

50%

Color-blind is a x-linked recessive trait, that means you need to have all the X chromosome have the defective genes.
Male genes is XY. Since the only male have Y gene so we can say for certain that the X gene is from the mother. The mother is heterozygous which means only have 1 of 2 defective genes. Then the chance for the mother to give defective gene is 50%.

A: rachel carson :