Allele distribution/ frequencies

Migration of individuals into a population can have a substantial impact on allele distribution stemming from two considerations. First, migration can act much like mutation except at a much higher frequency. That is, individ-... 

Goddard KA, Hopkins PJ, Hall JM, Witte JS. Hnkage disequilibrium and allele frequency distributions for 114 single-nucleotide polymorphisms in five populations. Am J Hum Genet 2000 66 216-234. 

Collie-Duguid ES, Pritchard SC, Pow-rie RH et al. The frequency and distribution of thiopurine methyltransferase alleles in Caucasian and Asian populations. Pharmacogenetics 1999 9 37-42. 

There are no circumstances for a gene with variation in Hardy-Weinberg equilibrium that will lead to equal numbers of individuals in each of the genotypic classes. Only in the case when allele frequencies are equal will the expected distribution be symmetrical. In such a case there will be equal numbers of the two homozygous classes (1/4 in each group), and 1/2 of the total sample will consist of heterozygotes. 

Rapid, accurate SNP validation can be carried out using a sample-pooling technique—allele frequency—that rapidly screens and confirms the presence of an SNP and its allelic frequency in patient populations. Conventional technologies typically analyze each SNP in each individual of the population in question, and individual results are then consolidated to yield the overall SNP allele-frequency distribution. MS-based technology is able to determine SNP allele frequencies with high precision in pooled samples, thereby replacing hundreds of individual measurements with one consolidated analysis. To that end, DNA is isolated, purified, and quantitated. A pool of DNA is formed from a high number of different individuals, amplified, and mass measured. 

Fig. 7. Frequency distribution of plasma Lp(a) concentrations (a) and apo(a) alleles (b) in three populations. Plasma Lp(a) levels were measured in 381 subjects by the sandwich ELISA technique apo(a) allele size (number of K-4 repeats) was estimated using pulsed-field gel electrophoresis and genomic blotting. [With permission of Gaw et at. (G11).]...

Population subsamples of American and African blacks, however, show a significantly different bell-shaped Lp(a) distribution (H6, P5, S40) (Fig. 7). The mean levels are twice those in Caucasians, indicating that the Lp(a) distribution depends upon race (G37). As there is an inverse relation between apo(a) size and plasma concentration, the distribution of different genotypes and allele frequencies is also dependent upon race (C6, Ml3). 

The APOE alleles show a peculiar distribution in the world (12,47,487). The APOE-3 allele is the most frequent in aU human societies, especially in populations with a long-established agricultural economy, such as those of the Mediterranean basin, where the allele frequency is 0.849-0.898. APOE-4 is the ancestral allele, with a frequency that stiU remains higher in Pygmies (0.407) and Khoi San (0.370), aborigines of Malaysia (0.240) and Australia (0.260), Papuans (0.368), some Native Americans (0.280), and Lapps (0.310), for whom an economy of foraging still exists or food supply is scarce or sporadically available. The frequency of the APOE-2 allele fluctuates with no apparent trend (0.145-0.02), is absent in Native Americans, and is very low (<1%) in southern Europeans (12,20,47,487-489). 

The distribution of ACE genotypes in the Spanish population was as follows ACE-I/I 14.8% in controls and 20.5% in AD ACE-I/D 45.6% in controls and 46.0% in AD and ACE-D/D 39.6% in controls and 33.5% in AD (623). In this study, a small increase in the frequency of ACE- allele was observed in LOAD (623). Nevertheless, as with many other polymorphic genes, some authors did not find association between the ACE-I/D polymorphism and AD in different populations (80,617,624-631). However, a meta-analysis of 12 case-control series published up to the year 2000 suggested that ACi genotypes are associated with AD (611), and that the ACE-D allele is more frequent in Spanish, American, and Russian AD patients than in controls (614,615,617) but not in the Italian and Jewish populations (627,632). 

De Olano, M., Fernandez-Novoa, L., Mesa, M.D., Corzo, L., Cacabelos, R. (2000) Different allelic frequency distribution in angiotensin-converting enzyme I/D polymorphism and angi-otensinogen M235T polymorphism in dementia. In Sixth International Stockholm/ Springfield Symposium Advanced Alzheimer Therapy, Stockholm, p. 202. 

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. 

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