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Inheritance of complex traits
Complex or multifactorial traits result from a combination of multiple genetic and environmental factors (such as lifestyle choices about diet and exercise), only some of which might be known. Accordingly, no single gene or environmental factor causes a complex trait.
Many birth defects, such as cleft lip and cleft palate, as well as many adult disorders, such as heart disease and diabetes, are examples of complex traits. Many complex traits are common – generally occurring in at least 1 out of every 1000 individuals.
Predicting an individual’s risk having a complex disease (i.e., risk of occurrence) or passing on a complex disease (i.e. recurrence risk) is difficult because each risk factor (whether genetic or environmental) contributes just a small part to an individual’s overall risk.