This is comparable to the conditions caused by mutations in single genes, which has an incidence range in close relatives of affected individuals to be between 25 and 50%. These conditions show a definite familial tendency, although the incidence in close relatives of affected individuals is usually within the range of 2 to 4%. On the other hand, multifactorial inheritance describes a trait whose manifestations are determined by two or more genes, accompanied by environmental factors. Effects of those genes are cumulative, in that no single gene is considered to be dominant or recessive to one another. It can be said that polygenic inheritance involves complex traits that are determined by many genes at different loci, without the influence of the environment. The term polygenic can have different meanings, including genetic effects that arise from the interaction of multiple genes. Image Credit: Dabarti CGI / Distinguishing polygenic and multifactorial disorders This is particularly true due to the fact that human diseases are often caused by a multitude of genetic and environmental factors acting in concert. In an age when the majority of monogenic human disease genes have been identified, one of the challenges for the coming generation of human geneticists will be to resolve complex polygenic and multifactorial disorders.
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