## Description

Haplotype blocks derived from common single nucleotide polymorphisms (SNPs) on chromosome 21 by Perlegen Sciences, as described in Patil, N. et al. Blocks of limited haplotype diversity revealed by high-resolution scanning. Science. 2001;294(5547):1719-1723.

The location of each haplotype block is represented by a blue horizontal line with tall vertical blue bars at the first and last SNPs of the block. Blocks are displayed as starting at the first SNP and ending at the last SNP of the block. This is slightly different from the representation on the Perlegen web site in which blocks are stretched until they abut each other. The shade of the blue indicates the minimum number of SNPs required to discriminate between haplotype patterns that account for at least 80% of genotyped chromosomes. Darker colors indicate that fewer SNPs are necessary. Individual SNPs are denoted by smaller black vertical bars. At multi-megabase resolution in dense display mode, clusters of tall blue bars may indicate hotspots for recombination.

For more information on a particular block, click "Outside Link" on the item's details page.

NOTE: Perlegen annotations appear only on chromosome 21.

## Credits

Thanks to Perlegen Sciences for making these data available.