Subsequent research has shown that tag SNPs chosen using the HapMap are generally applicable across other populations, but there are some limitations, particularly for rarer SNPs and for populations with substantial proportions of recent African ancestry (8). To allow better choice of tag SNPs and more detailed analyses for diverse populations, additional samples were collected from the same four initial HapMap populations and from seven additional populations: Luhya in Webuye, Kenya; Maasai in Kinyawa, Kenya; Tuscans in Italy; Gujarati Indians in Houston, Texas; Chinese in metropolitan Denver, Colorado; persons of Mexican ancestry in Los Angeles, California; and persons of African ancestry in the Southwestern United States (9). These 1301 extended HapMap samples are now available from the Coriell Institute and have been genotyped on the Affymetrix 6.0 platform and the Illumina 1 million SNP chip. Genome-wide sequencing of these samples to develop a comprehensive catalog of rarer variants will begin soon as part of the international 1000 Genomes Project (http://www.1000genomes.org).
