The fraction of variation (of an individual’s given trait) that is due to genetics. For example, if a pig’s trait (e.g., weight at birth) is 30% heritable, that means that 30% of the (birthweight) difference between that individual pig and its (statistically representative) group of contemporaries (pigs) is due to genetics. The other 70% would be due to factors such as nutrition of the mother during pregnancy, etc.
The degree to which a given trait is controlled by inheritance.
The proportion of a certain characteristic or trait, such as intellect, that can be attributed to genetic factors rather than to environmental ones.
Heritability is a measure of the degree to which a disease or disorder is influenced by genetic factors, as opposed to environmental influences like diet and climate. Some disorders, such as hemophilia or cystic fibrosis, are entirely caused by hereditary factors. On the other hand, certain disorders are solely the result of environmental factors. However, many disorders, like schizophrenia, lie between these extremes, where both inheritance and the environment likely play a role in their development.
An approximate measure of heritability can be derived by comparing the incidence of a disorder in the first-degree relatives (parents or siblings) of affected individuals with the incidence of the disorder in a population exposed to similar environmental influences. These estimates of heritability are valuable in the context of genetic counseling.