Heritability measures how important genetics is to a trait. A high heritability, close to 1, indicates that genetics explain a lot of the variation in a trait between different people; a low heritability, near zero, indicates that most of the variation is not genetic.
Heritability increases when genetics are contributing more variation or because non-genetic factors are contributing less variation; what matters is the relative contribution.
It defines heritability as the extent to which genetic individual differences contribute to individual differences in observed behavior (or phenotypic individual differences). You should memorize both of these definitions.
Narrow sense heritability describes the ratio of additive genetic variance to phenotypic variance. Genetic evaluation calculations use estimates of additive genetic variances. Using the average of several measurements of a phenotype can substantially increase heritability.
The selection response is how much gain you make when mating the selected parents. Remember, the narrow sense heritability is a measure of the genetic component that is contributed by the additive genetic variance. The response to selection can thus be dervied by multiply the heriability by the selection differntial.
Heritability is the single most important consideration in determining appropriate animal evaluation methods, selection methods and mating systems. Heritability measures the relative importance of hereditary and environmental influences on the development of a specific quantitative trait.
Heritability is a statistical measure that expresses a proportion of the observed variability in a trait that is a direct result of genetic variability.
A heritable trait is most simply an offspring's trait that resembles the parents' corresponding trait more than it resembles the same trait in a random individual in the population. Inheritance or heredity was a focus of systematic research before its inclusion as a key concept within evolutionary theory.
Negative heritability, then, could be perfectly sensible as a description of the data: It means that individuals with similar genotypes are likely to have more divergent trait values than those with highly disparate genotypes.
Heritability is expressed as H2 = Vg/Vp, where H is the heritability estimate, Vg the variation in genotype, and Vp the variation in phenotype. Heritability estimates range in value from 0 to 1.
A heritability score of 90% for height means that 90% of variation in height between members of the same population can be attributed to genetics. Environmental differences, then, like nutrition, exposure to pollutants, stress, etc.