What does the term "penetrance" refer to in genetics?

The term "penetrance" in genetics specifically refers to the likelihood that a person with a specific genotype will express the associated phenotype. This concept is crucial in understanding how genetic traits manifest in individuals. Penetrance is not simply about the presence of a gene but rather highlights the connection between genotype (the genetic makeup) and phenotype (the observable traits).

For instance, a gene may be present in an individual, but if the expression of the trait linked to that gene is not consistently observed across all individuals with the same genotype, this illustrates the concept of incomplete penetrance. Some individuals may carry a particular allele associated with a genetic condition, but that condition may not manifest in everyone with the genotype due to various factors such as environmental influences or interactions with other genes.

Understanding penetrance assists healthcare professionals in assessing risks and providing information about genetic conditions to patients and families. It underlines the complexity of genetic inheritance and expression, emphasizing that having a specific genetic variant does not guarantee that the associated trait will be observed in every individual.