They've pieced the story together using quite different strands of information, including the genomes of wild and cultivated bananas, the microscopic relics of banana leaf material found at archaeological sites, and even the word for 'banana' in different languages. Some scientists, in fact, have made a whole study of banana domestication and movement around the world. Having more than one gene of each type means that if one gene of a set loses function, the plant still has another one that works. Scientists don't know why, but they believe having extra copies of genes may have imparted some stability to plants during a time of rapid climate change after an asteroid hit Earth. Duplications like this are known to have happened in other plant groups at this same time but haven't occurred since, Heslop-Harrison said. Two of the doublings took place at the Cretaceous-Tertiary boundary 65 million years ago, back when the dinosaurs and lots of other species went extinct, Heslop-Harrison noted. And, intriguingly, three times since this genus of giant herbs took an evolutionary turn away from its relatives - the grasses - it has duplicated its entire set of chromosomes. There are whole sets of DNA repeats that plants normally have but bananas do not. There are remnants of bits of banana streak virus spliced into the banana genome (too broken-up to cause disease, however).
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