新托福阅读材料：Most human gene variations mapped

人类基因组最新研究

Leaders of a global project to catalogue differences in human DNA say they have successfully mapped 95% of all variations.

The 1000 Genomes Project aims to sequence and compare the DNA of 2,500 individuals from across the world.

Results also suggest each of us carry on average some 75 variations which may play a role in inherited disorders.

The initial findings, published in Nature, may offer new insights into disease and lead to new treatments.

Human catalogue

Coming a decade after the draft human genome was first published, the 1000 Genomes Project is a public-private project to map not one individual's genetic makeup but thousands of genomes.

The scientists behind it say it is only by mapping the differences in our genetic make-up that we can understand why some people may be more susceptible to inherited disease or other genetic conditions.

According to Dr Richard Durbin of the Wellcome Trust Sanger Institute, the project has only been made possible by improved technologies and the reduced cost of sequencing DNA.

"In the last 10 years DNA sequencing technology has advanced dramatically, so it's become feasible to systematically sequence many people to find genetic variants and build a catalogue which we can use as a basis for investigations into disease," he says.

An individual's genome is made up of some three billion "base pairs" of DNA, packaged up into 23 pairs of chromosomes that are found in each and every cell of our bodies.

Some three million of these base pairs vary from person to person; it is these so-called single nucleotide polymorphisms or SNPs that the scientists are trying to identify.

They already believe they have catalogued 95% of all the SNPs found in humans.

"Already, just in the pilot stage, we've identified over 15 million genetic differences by looking at 179 people," says Dr Durbin. "Over half those differences have never been seen before and these have already provided a more complete catalogue of variation than was available previously."

Results also suggest each individual on average carries some 75 variations which have been previously implicated in inherited diseases and between 250 and 300 which may result in some loss of function.

New methods

The project has used three different techniques to gather its information.

The genomes of 179 people from four different populations were sequenced partially, while samples from 697 individuals across seven populations were sequenced for genetic material that is responsible for encoding proteins across the body. At the same time, the DNA of two families was sequenced in depth.

The differing approaches reduced the overall cost and time required, but when taken and processed together create a highly sophisticated database.

Work on the full 1000 Genomes Project meanwhile continues, with all data being made accessible to scientists online.