This paper focuses on statistical methods that test for the effect of a single gene in a way that accounts for interaction with other genes. Such tests of association can be difficult since there may be many genetic and environmental factors that contribute to an effect. A gene is a hereditary DNA sequence that codes for a specific protein. A locus is a gene’s location in the DNA sequence of nucleotides (A, T, G, and C) and an allele is a specific version of a gene that has multiple forms. The existence of interactions between loci makes it difficult to determine the effect of a single genetic factor. Gene-gene interaction occurs when two genes together affect how a trait is expressed. That is, their combined effect is not the same as the sum of the two genes’ individual effects. If there are multiple genes that effect a genetic trait, then examining a gene in isolation without allowing for interactions may result in missing the gene’s effect. This is why allowing for interaction in a test of association can be more successful than tests that do not allow for interaction.
Smith, Clair, "A Comparison of Two Statistical Tests for Interaction in Genetic Data" (2014). WWU Honors Program Senior Projects. 6.