The threshold model explains the discontinuous distribution of some multifactorial traits. In this m

The threshold model explains the discontinuous distribution of some multifactorial traits. In this model, liability for a genetic disorder is distributed among individuals in a normal curve. This liability is caused by a number of genes, each acting additively. Only those individuals who have a genetic liability above a certain threshold are affected if exposed to certain environmental conditions. The severity of the disease usually increases as genetic liability moves away from the mean, and is affected by environmental factors.