A geneticist is studying the inheritance of a trait in humans. She observes that the offspring of two parents who are carriers of a recessive allele for a specific disease have a 25% chance of developing the disease. Which of the following is the most likely genotype of the affected offspring?

Core Concept

In a scenario where two parents who are carriers of a recessive allele have offspring with a 25% chance of developing the disease, the most likely genotype of the affected offspring is aa. This is because the only way for the offspring to express the disease is to be homozygous recessive.