Friday, February 01, 2008

Fresh Insight into Evolution

Studies of genetic recombination suggest that genetic shuffling varies by gender.

By Emily Singer

Genetic recombination: When cells divide to produce eggs and sperm, a process called meiosis, corresponding maternal and paternal chromosomes pair up and swap small pieces of DNA. (Paired chromosomes are depicted above.) This ensures a constant source of genetic diversity, which drives evolution. Credit: Technology Review

It's a tantalizing thought worthy of X-Men-inspired daydreams: are some of us, for better or for worse, evolving faster than others? Growing evidence suggests that rates of genetic recombination--one of the driving forces of human evolution--vary greatly between individuals. Two new studies shed further light on the inner workings of this gene-shuffling process, highlighting differences in the way men and women rearrange the DNA that they pass on to their children. The findings could help scientists understand disorders such as miscarriage and Down syndrome, which are linked to errors in recombination.

During recombination, corresponding maternal and paternal chromosomes align within cells and swap bits of DNA. These cells eventually develop into sperm and eggs, endowing future offspring with a different configuration of genes than their parents. "Recombination constitutes one of the most powerful means by which new combinations of genetic variants are generated in the genome," says Kari Stefansson, chief executive officer of deCODE Genetics, in Iceland, and senior author of one of the studies.

Previous research shows that recombination is often localized to specific spots on the genome, known as hot spots. Some people's genomes undergo this swap more than other people's, with apparently profound consequences. In 2005, Stefansson's group at deCODE found that women with higher recombination rates had more children, suggesting that evolution has selected for molecular mechanisms that create diversity.

Scientists study recombination by comparing genetic variation in parents and their children. New techniques to analyze huge numbers of genetic variations, commonly used to identify genes linked to disease, are now allowing a more detailed analysis of recombination than ever before. (See "Genes for Several Common Diseases Found.") In one such study, published Thursday in the online version of the journal Science, researchers from the University of Chicago generated a high-resolution map of recombination hot spots by analyzing the DNA of 725 people. The volunteers came from 82 families of Hutterites, a genetically similar group of European immigrants who settled in the Dakotas in the 19th century.