Across 1,000 genomes, rarities abound

Every person’s genetic instruction book is a trove of never-before-seen genetic variants, according to an ongoing effort to map human genetic diversity.

In recent years, scientists have discovered that humans carry far more rare genetic variants than anyone ever thought. Now, a major effort to map the diversity of humans’ genetic makeup — called the 1000 Genomes Project — has turned up even more variety than researchers had expected. The project has now lived up to its name, completing a comprehensive sampling of 1,092 people from 14 different populations around the world, an international consortium of researchers reports in the Nov. 1 Nature.

Among the anonymous people sampled, researchers found 38 million single DNA unit changes, known as SNPs. Of those, about two-thirds are newly discovered and many are rare, found in less than 0.5 percent of people. These variants, along with small and large insertions and deletions and rearrangements of DNA, may affect health and disease risk and can help scientists trace humans’ migrations around the globe.

 “The magnitude of rare variation observed in human populations has really been driven home to everyone,” says Nancy Cox, a quantitative human geneticist at the University of Chicago. Large numbers of rare variants in the 1,092 study participants indicate that human population growth has been “superexponential,” Cox says.