DNA jumps between animal species, but no one knows how often
A March paper in Trends in Genetics holds the unorthodox explanation: The gene became part of the smelt genome through a direct horizontal transfer from a herring. Laurie Graham, a molecular biologist at Queen's University in Ontario and lead author on the paper, knows she's making a bold claim in arguing for the direct transfer of a gene from one fish to another. Back in the early 2000s, Graham was studying AFPs under the direction of her lab leader Peter Davies when she was struck by the uncanny resemblance of the smelt protein's gene to one of the antifreeze genes produced by herring. In 2001, one of the major papers describing the newly sequenced human genome made extraordinary claims of horizontal gene transfers from bacteria based on comparisons to some animal genomes. Three of them flank the rainbow smelt's AFP gene, in the same order seen around the herring AFP gene. While these putative horizontal transfers were initially met with surprise, much as Graham's AFP gene was, the evidence is now undeniable. For context, it's worth noting that horizontal transfers can be hard to detect: Over time, ever more mutations accumulate in both the original and the recipient lineages, obscuring similarities in a shared gene.