A husband and wife have normal vision, although both of their fathers are red–green color-blind, an inherited X-linked recessive 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?

Key Concepts

X-linked Inheritance

X-linked inheritance refers to the pattern of inheritance for genes located on the X chromosome. In this case, red-green color blindness is an X-linked recessive trait, meaning that males (XY) are more likely to express the condition since they have only one X chromosome. Females (XX) can be carriers if they have one affected X chromosome but typically do not express the trait unless both X chromosomes are affected.

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two individuals. It helps visualize the possible combinations of alleles from each parent, allowing for the calculation of probabilities for traits in offspring. In this scenario, constructing a Punnett square will help determine the likelihood of their child being color-blind or having normal vision based on the parents' genotypes.

Genotype and Phenotype

Genotype refers to the genetic makeup of an individual, while phenotype is the observable expression of that genotype. In this question, the genotypes of the parents will influence the phenotypes of their children. Understanding the difference between these terms is crucial for predicting the traits of the offspring based on the parents' genetic information, particularly in the context of X-linked traits.