Inheritability (in genetics ) is the proportion of phenotypic variability in a population due to genetic variability (in relation to a specific qualitative or quantitative trait). Differences between individuals may be due to genetic factors and / or the environment. Inheritance analyzes the approximate ratio of the influence of genetic and non-genetic factors on the overall phenotype deviation in a population.
With heritability equal to 1, phenotypic variability is due only to genetic differences.
Content
Calculation of the Inheritance
For the quantitative characteristic of heritability, the value of the variance of the trait is used. The total variance ( V T ) can be represented as the sum of the variance associated with differences in the genotype ( V G ) and the variance associated with the influence of the medium ( V E ). It is usually assumed that the dispersion associated with the interaction of genotype and medium ( V I ) can be neglected. If all these assumptions are accepted, the total variance can be represented as
Inheritance is broadly understood as the coefficient of genetic determination ( H ²):
Features of the interpretation of the value of the genetic determination coefficient
It should be taken into account that the proximity of the value of H² to zero or one does not necessarily indicate the absence / presence of genetic control of this trait. For example, in inbred lines , where all members of a group are genetically homogeneous, the variability of a trait by definition will be controlled only by the environment. Conversely, when growing a group in absolutely homogeneous environmental conditions, all variability can be explained only by the influence of the genotype. The magnitude of heritability also varies between populations and depending on growing conditions.
Example of calculating genetic determination coefficient
In the described experiment, the research activity of mice of two genetically homogeneous inbred lines was studied: C57BR and A. Two generations of hybrid mice were obtained. The first child generation (F 1 ), like parents, is genetically homogeneous, since its individuals are heterozygous in all loci for which inbred lines differ and are homozygous in the rest. In the second generation (F 2 ), on the contrary, all possible genotypes are represented. The magnitude of the dispersions ( V ) are given in the table:
| Line of mice | Dispersion ( V ) |
|---|---|
| C57BR | 9.74 |
| A | 16.48 |
| F 1 | 12.23 |
| F 2 | 29.60 |
Dispersion in both parental lines and F 1 is ensured only by the influence of the environment ( V E ). To estimate the influence of the medium on the dispersion, the average for these three values is found ( V E = 12.82). In the F 2 generation, dispersion is associated with the influence of both the genotype and the environment ( V T ). According to the formula (1), the value of V G is equal to 16.78. Then the value of H², according to the formula (2), is equal to 0.57, that is, the variability of the research activity of mice is controlled by the genotype somewhat more than half.
Inheritance in the narrow sense
The true heritability ( h ²) is the ratio of the magnitude of the genetic additive dispersion ( V A ) to the total dispersion. By genetically additive dispersion is meant the part of V G that is associated with the action of dominant genes that suppress the manifestation of recessive alleles . From V G in this case, the effects caused by epistasis are excluded . Since V A is always less than or equal to V G , h ² will always be less than or equal to H ².
Literature
Dewsbury D. Genetics of behavior. In the book: Animal Behavior: Comparative Aspects / Trans. from English I.I. Poletaeva. M .: Mir, 1981. pp. 130-154.