What does a low heritability value mean?
A low heritability means that traits are not determined by genes” A heritability that is larger than 0 always indicates that genes have an effect on the expression of the phenotype. The heritability is determined by the proportion of genetic variance relative to the phenotypic variance.
A heritability close to zero indicates that almost all of the variability in a trait among people is due to environmental factors, with very little influence from genetic differences. Characteristics such as religion or language spoken have a heritability of zero because they are not under genetic control.
Heritability estimates are single numbers ranging from 0.0 to 1.0. An estimate close to 0.0 indicates very little contribution from genetics, while a heritability estimate close to 1.0 suggests that nearly all the variability in risk can be attributed to genetics, with little contribution from environmental factors.
Accuracy of selection for traits with low heritability can be improved with multiple measurements on an individual, use of pedigree information, and increased progeny group sizes.
For example, a trait with 70% or 0.7 heritability only means that a population's genetic differences account for 70% of the population's trait differences; the other 30% is caused by other factors.
Given its definition as a ratio of variance components, the value of heritability always lies between 0 and 1. For instance, for height in humans, narrow-sense heritability is approximately 0.8 (Macgregor et al., 2006).
In this example, let's say that we have determined the heritability of weight in this group of puppies is 0.3 (or 30%). This would mean that 30% of the variation in weight in the puppies is due to the particular genes each puppy inherited, and 70% of the variation is due to environmental (non-genetic) factors.
(HAYR-ih-tuh-BIH-lih-tee) The proportion of variation in a population trait that can be attributed to inherited genetic factors.
Narrow-sense heritability is defined as the fraction of phenotypic variance that can be attributed to variation in the additive effects of genes . Narrow-sense heritability is always less than or equal to broad-sense heritability.
Heritability is a measure of how much a trait's variation (such as the level of your mathematical intelligence) seems to be the result of the parents' physical characteristics, versus the effects of other factors, such as environment, exposure to stimuli, random chance, etc.