Scientists have succeeded in altering the patterns on a butterfly's wings by tweaking just one or two genes, an advance that may help understand how colour patterns and shapes evolved in the insects. By using the new method of CRISPR, a gene editing tool, researchers at Cornell University in the US cut out a gene known as spalt, and produced a butterfly lacking the large round markings known as eyespots. In another experiment, they removed a gene known as distal-less and produced more and larger eyespots. The experiments also produced changes in other parts of the wing. The distal-less gene in particular unveiled itself as a jack-of-all-trades gene that plays roles in shaping several parts of the body. Deleting it not only caused the butterfly to have extra eyespots, but to have shorter legs and antennae. "People suspected these genes had something to do with wing patterns but nobody had proved it," said Robert Reed, associate professor at Cornell University. "It probably takes dozens or hundreds of genes to make an eyespot, so it was remarkable to find that only one or two genes are required to add or subtract these complex patterns," said Reed. "It is a beautiful demonstration of how animals are assembled as modules, much like a model kit," he said. Butterfly wing patterns are of special interest to evolutionary biologists because they provide an easily accessible model of how natural selection chooses from many possible variations. The designs can be a defence against predators. Some butterflies are poisonous to birds (or maybe just taste bad) and birds can learn to recognise those by their designs. Other butterflies have evolved to mimic dangerous species. The large round markings on some butterfly and moth wings have come to be called "eyespots" because the spread out wings of the insect may look to a predator like the face of something big and dangerous. The designs also influence mate selection. The researchers worked with the butterflies Vanessa cardui, known as the "Painted Lady" or "Cosmopolitan" and Junonia coenia, the "Buckeye." The study was published in the journal Nature Communications.