THERE are millions of genetic variations between humans, and at the moment we don鈥檛 have a clue what differences, if any, most of these variations make to our brains and bodies. But the immense task of making sense of this genetic complexity is about to get a bit easier, thanks to a 鈥渕ap鈥� for working out which variations tend be inherited together.
That will give biologists a short cut. Instead of having to study variations one by one, they can look at the effects of patterns of variation. Ultimately, the aim is to discover why some people have a higher or lower risk of certain diseases, and how to tailor treatments to the individual.
Much of our genetic variation occurs in the form of single-letter changes in DNA, called single nucleotide polymorphisms or SNPs. There are an estimated 7 million sites in the genome for which at least two SNPs occur in the population at a frequency of 5 per cent or more. Researchers at Perlegen in Mountain View, California, have studied nearly 1.6 million common SNPs in 71 Americans of African, European and Chinese descent.
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Because neighbouring regions of a chromosome tend to be passed along as a unit from parents to offspring, identifying one SNP tells you which other SNPs are likely to be near it. The Perlegen team have calculated that with a subset of only 300,000 to 500,000 SNPs it is possible to predict any other SNP with more than 80 per cent accuracy (Science, vol 307, p 1072).
The findings, which Perlegen is making publicly available, should give geneticists a powerful tool for exploring the genetic underpinnings of diseases. 鈥淚t鈥檚 not an answer in and of itself. It is a tool to do more effective research,鈥� says Paul Cusenza, vice-president of alliance management at Perlegen.
鈥淭he same genetic variation can lead to different outcomes in people with different lifestyles鈥�
Other geneticists caution that understanding how genetic variations contribute to, say, heart disease will still not be easy. The same variation can lead to different outcomes in people with different lifestyles, for instance. 鈥淭he prospects are going to be improved, but whether it鈥檚 going to be wildly successful we don鈥檛 know,鈥� says geneticist Andrew Clark of Cornell University in Ithaca, New York.
And the maps can still be improved. Perlegen is now collaborating with a parallel, public effort known as the International HapMap Project to map SNPs in even greater detail based on the genomes of a larger number of people from around the world.
