This activity builds on information presented in the short film Genes as Medicine. Students interpret actual pedigrees to determine the inheritance pattern of Leber congenital amaurosis (LCA), an inherited form of blindness. They also examine protein sequence data to explore mutations that can cause LCA.

LCA is a disease that primarily affects the retina. Scientists have identified several types of LCA with different genetic causes and patterns of vision loss. In this three-part activity, students examine a form of LCA caused by mutations in the gene RPE65. 

The activity reinforces the connection between genotype and phenotype and illustrates that genes can have multiple alleles, including multiple disease-causing alleles. In the first part of the activity, students analyze several pedigrees of families with members who have LCA. The pedigrees were obtained from a published scientific study. In the second part, students explore mutations in the RPE65 protein in individuals with LCA and discover that some individuals (known as compound heterozygotes) carry two different disease-causing alleles. In the last part of the activity, students reflect on how LCA can be treated using gene therapy.