At least some sharks and skates have lost a collection of genes that was thought to be crucial to the survival of all jawed vertebrates.
Jawed vertebrates typically have four clusters of Hox genes, each containing up to 14 members, that are important in controlling embryonic development. Until now, complete deletion of any of these clusters had not been observed in a vertebrate.
Benjamin King of the Mount Desert Island Biological Laboratory in Salisbury Cove, Maine, and his colleagues found that the shark Scyliorhinus canicula and the skate Leucoraja erinacea (pictured) do not express genes found in one of these clusters, called HoxC. Sequencing of the L. erinacea genome confirmed that the genes were missing, as were two RNA fragments, called microRNAs, associated with the cluster.
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Case of a missing cluster. Nature 480, 416 (2011). https://doi.org/10.1038/480416a