Complex Traits

Just as with the genes themselves, which may act independently or together to cause a complex trait, genes and environmental factors may act independently or together to cause a complex trait. The actions can be additive, multiplicative, or epistatic.

One example of a multiplicative effect occurs in lung disease. Some people have a variation in the alpha-antitrypsin gene that moderately increases the chance that they will develop lung disease. However, if individuals with this variation also smoke regularly, they are at a greatly increased risk of getting lung disease, more than just smoking alone or just having the variation alone. Other cancer-related genes include tumor suppressor genes, whose particular alleles can influence the risk of developing breast cancer, for instance.