SNPing in the human genome

More than a million genetic markers in the form of single nucleotide polymo rphisms are now available for use in genotype-phenotype studies in humans. The application of new strategies for representational cloning and sequenci ng from genomes combined with the mining of high-quality sequence variation s in clone overlaps of genomic and/or cDNA sequences has played an importan t role in generating this new resource. The focus of variation analysis is now shifting from the identification of new markers to their typing in popu lations, and novel typing strategies are rapidly emerging. Assay readouts o n oligonucleotide arrays, in microtiter plates, gels, flow cytometers and m ass spectrometers have all been developed, but decreasing cost and increasi ng throughput of DNA typing remain key if high-density genetic maps are to be applied on a large scale.