What does penetrance of a trait refer to?

Penetrance of a trait refers to the percentage of individuals with a specific genotype who exhibit the expected phenotype. This concept is vital in genetics because it highlights that not all genotypes necessarily lead to the phenotypic expression one would expect based on Mendelian inheritance.

For instance, if a particular genetic condition is said to have 80% penetrance, it means that 80% of the individuals with the genotype associated with the condition will show the symptoms or characteristics of that condition, while 20% will not, despite carrying the same genetic information. This can occur due to a variety of factors, including the influence of other genes, environmental influences, or random biological variations.

Understanding penetrance is essential in predicting the likelihood of a trait being expressed in a population and can aid in genetic counseling and the study of hereditary conditions.