Genetic variation frequency

Essential to the definition of Pharmacogenetics is the term genetic polymorphism. It is extrapolated that there are at least three million genetic polymorphisms in the human genome. Historically, a genetic polymorphism was defined as a genetic variation with a population frequency of 1% and above, but the larger inter-ethnic variation of population frequencies makes a strict definition based on such frequencies impractical. The most common molecular type of polymorphism is the... 

Genetic drift is alteration of allele frequencies in small populations by chance events. During times when large populations are reduced to small numbers of individuals, genetic variation is likely to be lost by chance. Genetic drift also occurs when a small number of individuals colonize a new region. The pioneers are unlikely to have all the alleles found in the source population and the frequencies of the ones they do have are likely to differ from those in the source population. 

It is also important to understand the source and significance of genetic variations. The Pima Indians have the highest rates of diabetes in the world Tay-Sachs disease is primarily found in Ashkenazi Jews. Contemporary literature indicates that these differences stem from reproductive isolation, not race. Genetic traits common to persons with sickle-cell disease are related to malaria frequency and not our social view of race. This is why the disease can be found in high frequency in Yemen, West Africa, Greece, and Saudi Arabia. 

Population genetics has produced a detailed theory of the relationship between frequency, drift, and selective value of genetic variation (Nei, 1975 Hard and Clark, 1989 Li, 1997). The problem with its straightforward application is that the main parameters, such as history of population size, fixation rate, and selective pressure, are difficult to establish. 

An essential step in understanding genetic variation is to measure it in populations. This is done by estimating genotype and gene frequencies. 

Metabolic Enzyme" Genetic Variation (Alleles) Frequency of Genetic Variant [% and (Race )] Functional Consequence [% Frequency (Race ) in Population] Drug Substrate Implicated in Adverse Drug Reactions... 

By convention, polymorphisms are genetic variations where the least common allele or least common phenotype is present at a frequency of at least 1%. Human populations also display numerous genetic variations (termed rare genetic variants) that are present at a frequency lower than 1%. The major receptors that regulate induction of DMEs in humans (Table 1) exhibit few genetic variations that qualify as true polymorphisms (24). 

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