Nature Genetics
17, 435 - 438 (1997)
doi:10.1038/ng1297-435
Demographic history and linkage disequilibrium in human populationsMaris Laan1
& Svante Pääbo1
1Institute of Zoology, University of Munich, P.O. Box 202136, D-80021 Munich, Germany.
1e-mail: paabo@zi.biologie.uni-muenchen.de In the human genome, linkage disequilibrium (LD)—the non-random association of alleles at chromosomal loci1—has been studied mainly in regions surrounding disease genes on affected chromosomes2−6. Consequently, little information is available on the distribution of LD across anonymous genomic regions in the general population. However, demographic history is expected to influence the extent of overall LD across the genome, so a population that has been of constant size will display higher levels of LD than a population that has expanded7. In support of this, the extent of LD between anonymous loci on chromosome 4 in chimpanzees (as a model of a population of constant size) has been compared to that in Finns (as a model of an expanded population; refs 8,9) and found to exhibit more LD than in the latter population. In Europe, studies of mitochondria! (mt) DMA sequences have suggested that most populations have experienced expansion10, whereas the Saami in northern Fenno-Scandinavia have been of constant size (Table 1). Thus, in northern Europe, populations with radically different demographic histories live in close geographic proximity to each other. We studied the allelic associations between anonymous microsatellite loci on the X chromosome in the Saami and neighbouring populations and found dramatically higher levels of LD in the Saami than in other populations in the region. This indicates that whereas recently expanded populations, such as the Finns, are well suited to map single disease genes affected by recent mutations, populations that have been of constant size, such as the Saami, may be much better suited to map genes for complex traits that are caused by older mutations.
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