SNP haplotypes in white, African, Asian, and admixed populations from the 1000 Genomes. Continental populations may differ for the minor allele frequencies of SNPs, the strength of LD, and recombination, factors that define haplotype block structure within the MHC. Illustrated is the 20.8-kb TNF block consisting of the LTA-TNF-LST-NCR loci for samples from the 1000 Genomes Project Consortium^18,38  for individuals of diverse backgrounds. (A) White European, n = 379; (B) African, n = 246; (C) Asian, n = 286; and (D) admixed American (includes self-described Hispanic), n = 181. The intensity of the red color in each pairwise SNP comparison is a measure of the strength of LD as measured by D′.³⁹  Bright red boxes indicate a D′ of 1 (100% linkage), and the gradation of color to white indicates progressively smaller D′, values indicative of weaker LD. The different block structure and SNP haplotypes among these ethnically diverse populations may facilitate the fine mapping of SNP association signals within this region of the MHC.