Question

A husband and wife have normal vision, although both of their fathers are red-green color-blind, an inherited recessive X-linked condition. What is the probability that their first child will be a) a normal son, b) a normal daughter, c) a color-blind son, d) a color-blind daughter?

Answer 1

The first child of parents with normal vision, but carrying the colorblind gene, has a 50% chance of being a normal son, a 25% chance of being a non-carrier normal daughter (75% chance to be a carrier but normal), a 50% chance of being a color-blind son, and a 0% chance of being a color-blind daughter.

Step-by-step explanation:

The inheritance of red-green colorblindness, which is an X-linked recessive trait, is at the core of this question. We need to determine the genotypes of the parents. Since the husband and wife have normal vision and their fathers were colorblind, they both must carry one normal and one colorblindness gene. The mother's genotype is XNXc and the father's genotype is XNY, where XN represents a normal vision allele and Xc a colorblind allele.

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In summary, the son has a 50% chance of being colorblind or normal. The daughter cannot be colorblind but has a 25% chance of being a non-carrier of the colorblind gene and a 75% to be a carrier, while appearing normal due to the dominance of the normal allele.