A geneticist is studying the inheritance of a trait in humans. She observes that two siblings who are both affected with a specific disease are more likely to have children with the disease than two siblings who are not affected. Which of the following is the most likely explanation for this observation?

Core Concept

In a scenario where two siblings who are both affected with a specific disease are more likely to have children with the disease than two siblings who are not affected, the most likely explanation is that the disease is recessive and the siblings are carriers. This is because the siblings are more likely to pass on their recessive alleles to their offspring, increasing the chance of the disease being expressed.