Expression of concern: Subfunctionalization reduces the fitness cost of gene duplication in humans by buffering dosage imbalances.

After publication of this article (Fernandez et al., BMC Genomics 2011, 12:604) it was brought to the Editors' attention that the data generated by the first author, Ariel Fernandez, seemed anomalous. One of the author's institutions found that the data were not reproducible from the described methods, but an investigation by the author's other institution did not find the data or their interpretation suspicious. Given the conflicting conclusions of these investigations, the Editors advise the readers to interpret the data with due caution. We apologize to all affected parties.