Methods and apparatus for use in genetic trait classification involving at least two genes associated with a genetic trait are described. In one illustrative method, a value for use in classifying an individual into one of a plurality of trait classes associated with the genetic trait is calculated. The value is calculated based on (1) a sum of contributions associated with each genotype of a plurality of genotypes of the at least two genes identified for the individual, where the contributions for each genotype are identified at least in part from statistical associations between the genotypes and each trait class identified in a sample population; and (2) a sum of contributions associated with each one of one or more genotype combinations between the at least two genes identified in the individual, where the contributions for the one or more genotype combinations are identified at least in part from statistical associations between the genotype combinations and each trait class identified in the sample population. Advantageously, epistasis as well as additivity and dominance affects are taken into account for more accurate genetic trait classifications.