But some RNA viruses have an additional trick that further increases their capacity to evolve. They can recombine, swapping sections from one viral genome to another, like railroad trains switching cars on a siding. (Coronaviruses, for instance, recombine. Influenza viruses have their own version, called reassortment, with the breaks occurring at regular spots along their segmented genomes.) This occurs by a sort of molecular interruption during the process of replicating their genomes within the same cell. Recombination, Burke explained, “serves both to hybridize highly fit variants and to
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