This module introduces the concept of a complex phenotypes–a trait or disease such as height or diabetes where a large number of genetic variants contribute to the trait or to the risk of the disease. We introduce the standard linear additive model of phenotypes, using a normal distribution to understand the environmental influence on a trait. We discuss how the number of effects (betas) is equal to the number of variants under the additive model, but is intractably larger when there are gene by gene interaction. We introduce common subscripting conventions for writing out trait models and discuss the linear algebra representation.


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