Now THAT's a genome. A rare Japanese flower named Paris japonica sports an astonishing 149 billion base pairs, making it 50 times the size of a human genome—and the largest genome ever found. Until now, the biggest genome belonged to the marbled lungfish, whose 130 billion base pairs weighed in at an impressive 132.83 picograms. (A picogram is one-trillionth of a gram). The genome of the new record-holder, revealed in a paper in the Botanical Journal of the Linnean Society, would be taller than Big Ben if stretched out end to end. (The smallest genome known among organisms with nuclei is that of a mammalian parasite known as Encephalitozoon intestinalis, with a relatively paltry 2.25 million base pairs). The researchers warn however that big genomes tend to be a liability: plants with lots of DNA have more trouble tolerating pollution and extreme climatic extinctions—and they grow more slowly than plants with less DNA, because it takes so long to replicate their genome.

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