A woman with normal vision, but whose father was color blind, marries a color blind man. Suppose that the fourth child of this couple was a boy. This boy:

Explanation

The correct answer is that the boy may be color blind or may have normal vision. This is because the mother is a carrier of the color-blind allele (heterozygous), giving her son a 50% chance of inheriting either the color-blind allele or the normal vision allele. This illustrates the probabilistic nature of inheritance for X-linked recessive traits. Option B is incorrect because it assumes certainty of color blindness, which is not the case given the 50% probability. Option C is incorrect as it overlooks the possibility of inheriting the color-blind allele. Option D is incorrect because it misrepresents the genetic nature of X-linked traits; males are hemizygous and cannot be partially color blind.