An SNP map of human chromosome 22

The human genome sequence will provide a reference for measuring DNA sequen ce variation in human populations. Sequence variants are responsible for th e genetic component of individuality, including complex characteristics suc h as disease susceptibility and drug response. Most sequence variants are s ingle nucleotide polymorphisms (SNPs), where two alternate bases occur at o ne position (1-3). Comparison of any two genomes reveals around 1 SNP per k ilobase(1,3). A sufficiently dense map of SNPs would allow the detection of sequence variants responsible for particular characteristics on the basis that they are associated with a specific SNP allele(4-6). Here we have eval uated large-scale sequencing approaches to obtaining SNPs, and have constru cted a map of 2,730 SNPs on human chromosome 22. Most of the SNPs are withi n 25 kilobases of a transcribed exon, and are valuable for association stud ies. We have scaled up the process, detecting over 65,000 SNPs in the genom e as part of The SNP Consortium programme, which is on target to build a ma p of 1 SNP every 5 kilobases that is integrated with the human genome seque nce and that is freely available in the public domain.