Heritability

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The heritability ( "heritability" Symbol: h 2 ) is a measure of the heritability of properties in their phenotypic training both genes and environmental factors play a role. If a feature z. B. has a high heritability, the difference between two individuals can mainly be explained genetically. Heritability is basically applicable to all genetic properties; However, their practical application is almost only useful in the case of complex inheritance and traits with continuous development (such as body size, intelligence).

calculation

Selection difference (S) and selection success (R); h 2 = R / S.

For the calculation of heritability it is assumed that complex properties are normally distributed within a population and that a mean value therefore exists. By selection, you can now choose a subpopulation within the population, the mean value of which is different from the mean value of the initial population. This difference in mean values ​​is the selection difference.

If one now breeds with the individuals of the subpopulation, then in the population of their offspring a mean value of the property under consideration will again result. The difference between this mean value and the mean value of the starting population is the selection success.

The quotient of selection success and selection difference defines the heritability of the corresponding property. It fluctuates between 0 and 1 depending on the property, but it can also be specified in percent.

The prerequisite is that the same environmental conditions prevail during the rearing of the Parental and F1 generations, since otherwise the environmental influences on the expression of the measured properties will distort the calculated value for heritability.

There are also various estimation formulas for heritability (e.g. the Falconer formula or the Holzinger formula ).

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classification

Heritabilities are roughly classified as follows:

  • high heritability: over 0.45
  • Average heritability: 0.2 to 0.4
  • low heritability: 0.01 to 0.15

Applications

Livestock breeding

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

Human medicine and psychology

Estimates based on heritabilities are also sometimes used in humans to predict future performance. For example, in the former GDR, a method based on a heritability index was proposed for the prognosis of the future athletic performance of schoolchildren, for the purpose of selecting and specifically promoting future top athletes. The heritability of certain performance indicators, which had been assessed as decisive for the results in the respective sports, was estimated on the basis of a twin study (with monozygotic and dizygotic twins, determined on the basis of age and name equivalents in student lists). In this case, high heritability means that the corresponding performance should be traced back to an innate talent rather than to the previous level of training. The advantage of the heritability index compared to a longitudinal correlation , in which the performance of the same athletes is determined before and after the start of a targeted training, is the lower expenditure of time.

In contrast to animal breeding, such procedures are not very common in psychology, because, unlike in breeding, targeted experiments with complete control and manipulation of the respective environment are hardly feasible for practical and ethical reasons, so that one has to indirect methods, such as adoption or twin studies (as natural experiments ). It is unclear whether comparable methods were ever used outside the GDR.

Determination of the genetic basis

As described, the heritability of a trait is determined exclusively from the variance of the phenotypic traits. This means that the genetically (or possibly epigenetically ) determined proportion can be estimated in this way. So nothing is known about the underlying genes themselves. The most important method of determining the share of individual genes in heritability is carried out using quantitative trait loci .

literature

Individual evidence

  1. ↑ Volkmar Weiss (1981): The heritability index in the diagnosis of talent and aptitude in children and adolescents . Competitive Sports 11 (3): 192–195.
  2. ↑ Volkmar Weiss (1979): The heritabilities of athletic tests, calculated from the performance of ten-year-old twin pairs. Competitive Sports 9 (1): 58-61.

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