The magic number

日期:2019-03-07 03:07:02 作者:罗喱遇 阅读:

By Jeff Hecht HOW did insects come to have only six legs? American developmental biologists have now answered this question. By inactivating two genes, they persuaded beetle larvae to sprout 16 extra legs, recreating limbs their ancestors lost around 400 million years ago. Insects and other arthropods evolved from animals resembling modern millipedes and centipedes, which have many separate, unspecialised body segments, each with their own pair of legs. In insects, six segments fused to make the head, three with two legs each formed the thorax,