Genetic variance

Ronald Fisher in 1913

Genetic variance is a concept outlined by the English biologist and statistician Ronald Fisher in his Fisher's fundamental theorem of natural selection which he outlined in his 1930 book The Genetical Theory of Natural Selection which postulates that the rate of change of biological fitness can be calculated by the genetic variance of the fitness itself.[1] Fisher tried to give a statistical formula about how the change of fitness in a population can be attributed to changes in the allele frequency. In his 1997 paper Lessard pointed out that Fisher had made no restrictive assumptions in his formula concerning fitness parameters, mate choices or the number of alleles and loci involved.[2]

The genetic variance is usually the phenotypic variance that are combined the genotype variance with the environmental variance. The genetic variance has three components: the additive genetic variance, the dominance variance, and interactions. The interactions can be epistatic effects among the individual quantitative traits and the effect of the environment on gene expression.[3]

Additive genetic variance, refers to the deviation from the mean phenotype due to inheritance of a particular allele and this allele's relative (to the mean phenotype of the population) effect on phenotype. The dominance genetic variance, involves deviation due to interactions between alternative alleles at a specific locus. The Epistatic variance—involves an interaction between alleles; however, in this case, the alleles are associated with different loci.[4]

Quantitive Formula

All instances of phenotypic variance (VP) within a population are the result of genetic sources (VG) and/or environmental sources (VE).

VP = VG + VE[5][6]

VP = total phenotypic variation of the segregating population

VG = genetic variation that contributes to the total phenotypic variation

VE = environmental contribution to the total phenotypic variation

Genetic sources of variation can themselves be divided into several subcategories, including additive variance (VA), dominance variance (VD, and epistatic variance (VI). Together, the values for each of these subcategories yield the total amount of genetic variation responsible for a particular phenotypic trait:

VG = VA + VD + VI[7]

Measuring method

1.Genetic variance–covariance (G ) matrices conveniently summarize the genetic relationships among a suite of traits and are a central parameter in the determination of the multivariate response to selection.[8]

2. Using a single-nucleotide polymorphisms (SNP) regression method to quantify the contribution of additive, dominance, and imprinting variance to the total genetic variance[9]

Research Examples

1.The distribution of genetic variance across phenotypic space and the response to selection.[10]

Understand how empirical spectral distribution of G predicts the response to selection across phenotypic space. In particular, trait combinations that form a nearly null genetic subspace with little genetic variance respond only inconsistently to selection. They set out a framework for understanding how the empirical spectral distribution of G may differ from the random expectations that have been developed under random matrix theory (RMT). Using a data set containing a large number of gene expression traits.

References

  1. ↑ Perspective: Here's to Fisher, additive genetic variance, and the fundamental theorem of natural selection. By Crow JF, published in Evolution, July 2002
  2. ↑ Fisher's Fundamental Theorem of Natural Selection Revisited by Sabin Lessard
  3. ↑ MONNAHAN, PJ; KELLY, JK. Epistasis Is a Major Determinant of the Additive Genetic Variance in Mimulus guttatus. PLoS Genetics. 11, 5, 1-21, May 2015. ISSN 1553-7390
  4. ↑ Byers, D. (2008) Components of phenotypic variance. Nature Education 1(1):161
  5. ↑ Falconer, D. S., & Mackay, T. C. F. Introduction to Quantitative Genetics (London, Longman, 1996)
  6. ↑ Lynch, M., & Walsh, B. Genetics and Analysis of Quantitative Traits (Sunderland, MA, Sinauer Associates, 1998)
  7. ↑ Byers, D. (2008) Componentsof phenotypic variance. Nature Education 1(1):161
  8. ↑ Lande, R., 1979 Quantitative genetic-analysis of multivariate evolution,applied to brain-body size allometry. Evolution 33: 402–416
  9. ↑ Blows, M. W. and McGuigan, K. (2015), The distribution of genetic variance across phenotypic space and the response to selection. Molecular Ecology, 24: 2056–2072. doi:10.1111/mec.13023
  10. ↑ BLOWS, MW; MCGUIGAN, K. The distribution of genetic variance across phenotypic space and the response to selection. Molecular Ecology. 9, 2056, 2015. ISSN 0962-1083

External links


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