<P> Quantitative genetics focuses on genetic variance due to genetic interactions . Any two locus interactions at a particular gene frequency can be decomposed into eight independent genetic effects using a weighted regression . In this regression, the observed two locus genetic effects are treated as dependent variables and the "pure" genetic effects are used as the independent variables . Because the regression is weighted, the partitioning among the variance components will change as a function of gene frequency . By analogy it is possible to expand this system to three or more loci, or to cytonuclear interactions </P> <P> When assaying epistasis within a gene, site - directed mutagenesis can be used to generate the different genes, and their protein products can be assayed (e.g. for stability or catalytic activity). This is sometimes called a double mutant cycle and involves producing and assaying the wild type protein, the two single mutants and the double mutant . Epistasis is measured as the difference between the effects of the mutations together versus the sum of their individual effects . This can be expressed as a free energy of interaction . The same methodology can be used to investigate the interactions between larger sets of mutations but all combinations have to be produced and assayed . For example, there are 120 different combinations of 5 mutations, some or all of which may show epistasis...</P> <Table> <Tr> <Td> </Td> <Td> This section is empty . You can help by adding to it . (May 2014) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section is empty . You can help by adding to it . (May 2014) </Td> </Tr>

What is the role of epistasis in inheritance