Allele distribution/ frequencies changes

Enzyme levels and activities within the human population can vary considerably and many of the enzymes involved in the metabolism of xenobiotics are polymorphicaUy distributed in the human population. Genetic polymorphism (from Greek poly many , morph form ) is defined as the occurrence of at least two different alleles, with allele frequencies exceeding 1% at a particular locus. The allelic variants include point mutations as well as deletions and insertions and genetic polymorphism may cause an increase, a decrease, or no change in enzymatic activity. 

Chan CW, Chang JK The role of Chinese medicine in New York City s Chinatown. Am J Chin Med 4 31-45,129-146,1976 Chang FM, Kidd JR, Livak KJ, et al The world-wide distribution of allele frequencies at the human dopamine D4 receptor locus. Hum Genet 98 91-101,1996... 

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