Form a small discussion group and decide on the most likely genetic explanation for each of the following situations;

A man who has red–green color blindness and a woman who has complete color vision have a son with red–green color blindness. What are the genotypes of these three people, and how do you explain the color blindness of the son?

Key Concepts

X-Linked Inheritance

Red-green color blindness is an X-linked recessive trait, meaning the gene responsible for this condition is located on the X chromosome. Males, having one X and one Y chromosome, express the trait if their single X carries the allele for color blindness. Females, with two X chromosomes, must have the allele on both Xs to express the trait, making them less likely to be color blind.

Genotype of the Individuals

In this scenario, the man with red-green color blindness has the genotype X^cY, where X^c represents the X chromosome with the color blindness allele. The woman with complete color vision can be either X^cX (carrier) or X^NX^N (homozygous normal). Their son, who has red-green color blindness, must inherit the X^c from his mother and the Y from his father, resulting in the genotype X^cY.

Punnett Square Analysis

A Punnett square can be used to predict the genotypes of offspring based on the parents' genotypes. In this case, if the mother is a carrier (X^cX^N), the Punnett square will show a 50% chance of the son being color blind (X^cY) and a 50% chance of having normal vision (X^NY). This tool helps visualize the inheritance patterns and probabilities of traits in offspring.