Biallelic polymorphism

C, Charmley P, Kaiser R, Hood L. Identification of clusters of biallelic polymorphic sequence-tagged sites (pSTSs) that generate highly informative and... 

Ul. Underhill, P. A., Jin, L., et al. Detection of numerous Y chromosome biallelic polymorphisms by denaturing high-performance liquid chromatography. Genome Res. 7(10), 996-1005 (1997). 

There is evidence implicating alpha-adrenoceptors in hypersalivation caused by clozapine, and it has been hypothesized that a biallelic polymorphism in the promoter region of the alpha2-adrenoceptor gene confers susceptibility to schizophrenia, which is associated with a clozapine-induced favorable therapeutic response and/or clozapine-induced hypersalivation (172). However, the results in 97 patients showed that the alpha2-adrenoceptor gene polymorphism did not play a major role in susceptibility to hypersalivation or the therapeutic response of patients with schizophrenia. 

Fig. 12. HuSNP array design. A A known biallelic polymorphism at position 0 is interrogated by a block of four or five probe sets (five in this example). Each probe set consists of fonr probes, a perfect match and a mismatch to allele A, and a perfect match and a mismatch to allele B. One probe set in a block is centered directly over the polymorphism 0 ), and others are centered upstream (-4,-1) and downstream (+1, +4). B The sequences of the prohe set centered over the polymorphism is shown. C Sample images of Mocks showing homozygous A, heterozygous A/B, or homozygous B at the same SNP site. (Reprinted with permission from Warrington JA et al (2000) In Microarray biochip technology. Biotechniques Books, p 122)...

Allele One form of a genetic locus, distinguished from other forms (= alleles) by its particular nucleotide or its coded amino acid sequence. Single nucleotide polymorphisms are biallelic, i.e., one base pair is exchanged with just one other base pair. In such a case, only two different alleles exist in the population for such a gene locus. However, several different alleles may exist in the population if the locus is defined by more than one nucleotide (i.e., microsatelhtes, haplotypes). Thus,... 

If in a DNA or protein sequence a single position is variant, this may be called a polymorphism or mutation. The difference is set by convention a mutation is rare, and a polymorphism is common. By implication, a mutation may be deleterious, or in rare cases it may be advantageous for the reproductive fitness of its carriers. A widespread polymorphism, on the other hand, is unlikely to affect the fitness to such an extent. A frequency value of 1 % of the polymorphic allele is usually taken as a threshold between mutation and polymorphism (Ki-mura, 1983 Li, 1997). A polymorphic site is called biallelic if two variants segregate in the population, and multiallelic if there are more than two variants, which is a rare event in human sequences. 

Both articles included comparative studies on ape genomes in an attempt to reveal information on the evolutionary age of polymorphisms. If at a biallelic site one allele is present in the related species, it thought to be the ancestral allele. In most cases the more frequent allele was also the ancestral one, although there were exceptions with the less frequent allele being that of the chimpanzee (this was ascribed to drift... 

Nicod J, Bruhin D, Auer L, Vogt B, Frey FJ, Fer- 2092. rari P (2003) A biallelic gene polymorphism of CYP11B2 predicts increased aldosteroneto renin... 

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