Landmarks of Human Variations
Surveys of human haplotypes lend support to a sometimes criticized
international effort
By Maria W. Anderson

The myriad medical breakthroughs predicted to come from the sequencing of
the human genome have yet to pour freely. The idea that genes related to
common diseases and unique drug responses can be uncovered through careful
scrutiny of genetic variation is an inspiring one, but searching for
variability remains expensive and time-consuming. A project that would map
variants common in most human populations might ease that search. In July
2001, five months after publication of the draft sequence, the National
Institutes of Health started planning such a project, now known as the
International HapMap Consortium.

This issue's Hot Papers provided scientific support for the ideas behind the
HapMap Project: that genetic variation found among a few human populations
could be divided into manageable and predictable chunks and extrapolated to
people around the world in order to identify variability responsible for
common diseases. In their November 2001 paper, David Cox, Nila Patil, and
colleagues at Perlegen Sciences of Mountain View, Calif., describe the
structure of linkage disequilibrium (LD), or the correlation between alleles
at different loci, along chromosome 21.1 They found that the chromosome
comprised 4,135 blocks, 589 of which contained 10 or more single nucleotide
polymorphisms (SNPs) and covered more than 44% of the chromosome. Seven
months later David Altshuler, Stacy Gabriel, and others from the Whitehead
Institute/MIT Center for Genome Research (now the Broad Institute) published
a similar study2 examining 51 autosomal regions across the whole genome and
showing that haplotypes can be identified by genotyping a selection of
common markers, without resequencing the whole genome.

Both groups reached the same three conclusions. Millions of SNPs in the
genome are associated with their neighbors in haplotype blocks, a dozen or
more kilobases long. Moreover, between 65% and 85% of the human genome is
organized in such blocks. Finally, each block comes in three or four common
versions that capture the majority of genetic diversity throughout the
entire human population.

Read the rest at The Scientist.com
http://www.the-scientist.com/yr2004/may/hot_040510.html

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