Single nucleotide polymorphisms (SNPs) are the basic units of genetic variability that create much of what is unique about individual's propensity for disease and range of responsiveness to drug therapies. Researchers have found that, in some populations, SNPs travel in groups eight times as large as was previously thought. The work suggests that it is eight times easier to map genes for common, multigenic diseases, and paves the way for whole genome comparisons between normal controls and unrelated disease patients to detect the genetic basis of common diseases. Researchers say there are enough publicly available SNPs to create a genome wide SNP marker map, and that the bottleneck to disease gene identification now lies in genotyping.
Researchers at the Whitehead Institute/MIT Center for Genome Research (Cambridge, MA) and the Institute of Biological Anthropology at the University of Oxford (Oxford, UK) investigated linkage disequilibrium (LD), or associations between neighboring alleles in the genome. LD reflects the degree to which gene variants are not randomly distributed in the genome. It can arise because of selection or population history. While the extent of LD decreases in proportion to the number of generations since the LD-generating event, it can also be increased by populations interbreeding. We would expect to see short LD—shown by a short region occupied by a particular group of SNPs—in populations that have experienced long-term uninterrupted expansion. Equally, long LD would suggest a relatively new population that has arisen from what was once only a few people.
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