The haplotype patterns for 20 independent globally diverse chromosomes defined by 147common human chromosome21 SNPs. The 147SNPs span 106 kb of genomic DNA sequence. Each row of colored boxes represents a single SNP. The blue boxes in each row represent the major allele for that SNP, and the yellow boxes represent the minor allele. Absence of a box at any position in a row indicates missing data. Each column of colored boxes represents a single chromosome, and the SNPs are arranged in their physical order on the chromosome. Invariant bases between consecutive SNPs are not represented in the figure. The147 SNPs are divided into18 blocks, defined by black horizontal lines. The position of the base in chromosome 21 genomic DNA sequence defining the beginning of one block and the end of the adjacent block is indicated by each number to the left of the vertical black line. The expanded boxes on the right of the figure represent a SNP block de-fined by 26 common SNPs spanning 19 kb of genomic DNA. Of the seven different haplotype patterns represented in the sample, the four most common patterns include 16 of the 20 chromosomes sampled (i.e., 80% of the sample). The blue and yellow circles indicate the allele patterns of two SNPs, which unambiguously distinguish the four common haplotypes in this block.