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 the-the-Open ↗
scientist.com/yr2004/may/hot_040510.html
Posted by Robert Karl Stonjek.