Heritability

The heritability (symbol: h2) is a measure of the heritability of properties, both genes and environmental factors play a role in the phenotypic education. Although it is in principle applicable to all genetic characteristics; their practical application is useful but almost only in complex Erbgängen and continuous phenotypic expression.

Calculation

For calculating the heritability is assumed that complex properties are normally distributed within a population and that therefore there is a mean value. By selection can now be selected within the population a subpopulation with a mean value of the mean of the parent population is different. This difference between the means is the selection differential.

Culturing now with the individuals of the subpopulation as a mean value of the observed property is located in the population of their offspring in turn result. The difference between this average and the average of the initial population is the selection response.

The ratio of selection response and selection differential defines the heritability of the corresponding property. It varies depending on the property between 0 and 1, but can also be specified as a percentage.

For the heritability there are also different estimation formulas (eg, Falconer 's formula or the Holzinger formula).

Classification

Heritabilities are classified approximately as follows:

- High heritability: about 0.45 - Medium heritability: 0.2 to 0.4 - Low heritability: 0.01 to 0.15

Applications

Livestock breeding

Heritabilities are today mainly used in livestock breeding. Main application areas are muscle growth, meat quality and milk yield in the food production and prize money in sport horses. In particular, they play an important role in the breeding value estimation.

Human medicine and psychology

In human medicine, and psychology in particular, identical twins are suitable for heritability estimates. The following procedure is common:

Without measurement error and environmental influences would have identical twins have identical values ​​, ie a correlation of the measured values ​​of 1.00 and a heritability of 1.00. Show twins deviations at the time a must, on the environmental influences (including learning ) based who were active prior to the time a and spawned differences, and measurement errors, and influences that are present at time a. The assumption that such differences and sources of error of comparable magnitude in the future, will be available by the time b, seems plausible and practically useful. Thus, an analogy to the results in longitudinal section correlation with the relationship between two values ​​at the time points A and B is quantified. This can be derived from the measured values ​​at the time a, weighted by the heritabilities, appreciate the measured values ​​at the time b and their statistical reliability.

The difference between longitudinal studies and heritability estimates is that in longitudinal studies the longitudinal correlation is measured and calculated directly as a measure of the statistical relationship between two measurements at different times, of the heritability of the deviation and the mean value of the results from the genetic theory of correlations between population members same state of affairs is accessible by two measurements at the same time indirectly.

For certain practical problems provides the heritability compared with the longitudinal correlation Advantages: longitudinal cuts take years, heritability can be with twins or relatives correlations appreciate very quickly and use, for example in fitness diagnostics, the final values ​​can be taken from cross-sections.

If the linear combination is determined ( by regression equations) the suitability variables with the defined criterion (occupational performance, athletic performance, IQ, etc.) and the intercorrelations of the suitability variables are known, so can a suitability index as Heritabilitätsindex calculate the heritabilities as prognostic weights the measured values ​​received.

Such methods have come in the forecast of sporting excellence on the application.

Determining the genetic basis

The heritability of a trait, as described, being determined solely from the variance in the phenotypic characteristics. This means that the genetic ( or possibly epigenetic ) determinate share in total can be estimated. This is about the underlying genes themselves not yet known. The main way to determine the proportion of individual genes on the heritability, is via quantitative trait loci.