Take any two individuals, sequence and compare their genomic DNA, and you'll find that the vast majority (about 99.9%) of the sequences are identical. In the remaining 0.1% lie differences in disease susceptibility, environmental response, and drug metabolism. Researchers are understandably keen to dissect these variations, most of which take the form of single-nucleotide polymorphisms (SNPs).
A SNP (pronounced "snip") is a substitution of one base pair at a given location on the genome. At position 11,294,479 on human chromosome 7, for instance, some people have an A, while others have a G. On average, SNPs are spaced every 300 bases throughout the human genome and are estimated at nearly 10 million. Each is a genomic landmark, a surveyor's marker that researchers can use to chart the location of disease genes and heritable traits, for instance.
Most SNPs reside outside coding regions, exerting potential influence on gene regulation and expression. ...
