Some common multifactorial disorders include schizophrenia, diabetes, asthma, depression, high blood pressure, Alzheimer's, obesity, epilepsy, heart diseases, Hypothyroidism, club foot, cancer, birth defects and even dandruff.
The quick change in the patterns of morbidity, within one or two generations, clearly demonstrates the significance of environmental factors in the development and reduction of multifactorial disorders.
[10] Environmental risk factors include change in life style (diet, physical activity, stress management) and medical interventions (surgery, drugs).
[11] Autosomal or sex-linked single gene conditions generally produce distinct phenotypes, said to be discontinuous: the individual either has the trait or does not.
[citation needed] An example of how the liability threshold works can be seen in individuals with cleft lip and palate.
[citation needed] Francis Galton was the first scientist who studied multifactorial diseases and was the cousin of Charles Darwin.
When a trait (human height) exhibiting continuous variation is plotted against a graph, the majority of population distribution is centered around the mean.
[16] The traits exhibiting discontinuous variation, occur in two or more distinct forms in a population as Mendel found in color of petals.