Human variation chalked up to natural selection: study

By comparing millions of fragments of genetics code from individuals in four groups -- from Nigeria, China, Japan and northwestern Europe -- they showed that natural selection has played a key role in these differences, according to the study.

The findings hold particular promise for understanding the genetic underpinning of certain diseases.

The researchers, led by Lluis Quintana-Murci of France's National Centre for Scientific Research pinpointed, for example, the tiny genetic variation in the CR1 gene that has made 85 percent of Africans highly resistant to malaria.

Most other populations in the world do not share this variant, and are thus more susceptible to the mosquito-borne disease.

Other genetic variations -- called single nucleotide polymorphisms, or SNPs (pronounced "snips") -- identified by Quintana-Murci and his team could help explain why rates of diabetes, obesity and hypertension differ from one region to another.

Once the specific bit of genetic code responsible for a predisposition to a certain illness or condition has been identified, scientists can then set about trying to find a drug to treat it.

SNPs occur when one of the four chemical building blocks of DNA varies in a particular segment of DNA as compared to other members of the same species.

Some of these genetic mutations have happened through positive selection, which means they provide an advantage in the struggle to survive.

Being resistant to malaria is more useful in sub-Saharan Africa than in Norway, for example.

Others are driven by negative selection, the process by which genetic traits are forced out of a species because they impede survival.

The study, based on the international HapMap catalog of genetic variants within and among populations around the world, found SNPs that account for differences in eye and hair color as well.

"These genes played a role in adapting to our environment, and their mutation gave rise to certain advantages," said Quintana-Murci.

"But the genes that explain the phenotypic differences between populations only represent a tiny part of our genome, confirming once again that the concept of 'race' from a genetic standpoint has been abolished," he added.

Genotype is the genetic blueprint contained in DNA, while phenotype is the individual organism brought into being based on the instructions contained in that DNA.

The study, published in Nature Genetics, identified 582 genes that mutated through natural selection, probably between 10,000 and 60,000 years ago.

© 2008 AFP