What does the term "penetrance" refer to in genetic terms?

Penetrance is a fundamental concept in genetics that refers to the proportion of individuals with a specific genotype who actually express the corresponding phenotype. This means that for a particular genetic trait, not everyone who possesses the genotype will exhibit the observable characteristics associated with it. This property can vary among different populations and under different environmental conditions, leading to situations where some individuals exhibit a trait while others do not, even though they share the same genetic predisposition.

For example, if a particular gene is associated with a trait, and 80% of individuals with that gene show the trait, we would say that the penetrance of that gene is 80%. This concept is particularly important when studying inherited diseases, where some individuals may carry a mutation linked to a disease but do not show symptoms due to incomplete penetrance.

In contrast, the other options relate to different genetic concepts. The range of phenotypes expressed pertains to variability in traits rather than the proportion of individuals showing a trait. Specific gene location refers to the chromosomal position of a gene, while the inherited sequence of nucleotides describes the genetic code itself, rather than its expression or penetrance in a population.