For the first time in humans, researchers have discovered a large chromosomal rearrangement that bears the mark of natural selection, they report in the February issue of Nature Genetics.

The rearrangement, a 900-kilobase inversion polymorphism, appears in two distinct lineages, H1 and H2, that have diverged for as long as 3 million years with no evidence of having recombined. The H2 lineage—which is rare in Africans, almost nonexistent in East Asians, but found in 20% of Europeans—appears to undergo positive selection in Iceland, with carrier females having 3.2% more children per generation and higher recombination rates.

"This raises the question of how many such inversions remain to be discovered in the genome and what their effects might be," study co-author Kari Stefansson, chief executive officer of biopharmaceutical company deCODE Genetics in Reykjavik, Iceland, told The Scientist. The mechanisms for the increased fertility and recombination rates remain uncertain and...

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