Additive genes are genes that code for the same function that has a wide range of phenotypes. This allows for a wide ranges of phenotypes based on genetic coding.1 Additive genes are independent of other genes and when coupled with non-additive genes, are the result of genetic variance.2
4. Example of additive genetic variance.
Additive genes are related to epistasis because they contribute to epistatic effects - the presence of an additive gene can change the way other alleles act.2
The environment can have an effect on additive genes - stress can change additive genetic variance and can increase heritability.3
1. Biology Online (2005). Additive Genes. Retrieved from http://www.biology-online.org/dictionary/Additive_Genes
2. Show, Carson (2013). Heritability and Additive Genetic Variance. Retrieved from https://sciencehouse.wordpress.com/2013/10/04/heritability-and-additive-genetic-variance/
3. Blows, M and Sokolowski, M (1995). The Expression of Additive and Nonadditive Genetic Variation Under Stress. The Genetics Society of America. Retrieved from http://www.genetics.org/content/140/3/1149.full.pdf
4. Additive Trait (n.d.). Retrieved from http://www.glenn-apiaries.com/images/smradd.gif