What does variable expressivity refer to in genetic conditions?

Variable expressivity refers to the phenomenon where individuals with the same genetic mutation may exhibit a range of symptoms or varying severity of a condition, even though they share the same genetic basis for the disorder. This means that while two individuals may have the same genetic condition, one may experience mild symptoms, while the other may have severe manifestations. The differences in symptom severity can be influenced by various factors, such as the influence of other genes, the environment, age, and lifestyle choices. This concept is crucial in genetics because it highlights the complexity of genetic diseases and the importance of personalized medicine—where treatment may need to be tailored to the individual based on their specific symptoms and condition severity.

The other options describe different concepts in genetics, such as polygenic traits, the co-occurrence of disorders, and environmental influences on gene expression, which do not specifically define variable expressivity.