PLoS Biol. 8, e1000327 (2010)

Near the centre of a chromosome lies the centromere, a region where thin protein fibres attach to pull chromosomes apart during cell division. Unlike other parts of the chromosome, the centromere rarely, if ever, experiences crossover — the exchange of genetic material between two chromosomes of a pair. Yet the centromere is one of the most diverse structures of the genome. Kelly Dawe at the University of Georgia in Athens and his colleagues have discovered one mechanism that may have helped this diversity to arise.

They mapped 238 centromere markers from 93 maize (corn) lines and found no crossing over but observed two instances of gene conversion, in which a short piece of DNA from one chromosome is copied onto another. They also found that, at least in maize, gene conversion occurs frequently, which may explain the high level of centromere diversity.