Scientists Identify the Genes That Paint Butterfly Wings

There are some 20,000 species of butterflies fluttering in skies around the world—each one with its own uniquely beautiful wings filled with spots, stripes, colors and more in seemingly every imaginable pattern. Scientists have long assumed that these complex designs were governed by an equally complex series of genes, similar to traits like human eye color. But new research suggests that may not be the case.

In two related studies published this week in the Proceedings of the National Academy of Sciences, researchers identified just two genes that play a major role in making wings look the way they do. It's the first step toward scientists gaining the ability to paint the wings of butterflies themselves.

To determine how these genes work, the scientists tried to interfere in wing design, reports Rachael Lallensack for Nature. Using the CRISPR-Cas9 gene editing system—which functions like a pair of genetic scissors—the researchers disabled these genes in the eggs of various species to see what effect they had on how the wings of the butterflies developed.

"Imagine a paint-by-number image of a butterfly," Owen McMillan, a zoologist with the Smithsonian Tropical Research Institute, says in a statement. "The instructions for coloring the wing are written in the genetic code. By deleting some of the instructions, we can infer which part says 'paint the number twos red' or 'paint the number ones black.'"

The results of one of the new studies, co-authored by McMillan, demonstrate just how much one of the controlling genes, known as WntA, controls the "painting." The butterflies with the disabled gene looked far different than their normal brethren—the colors appear splotchy, no longer contained in tightly lined patterns. And some of the markings disappeared, reports Ben Guarino for the Washington Post. The WntA seems to lay the groundwork for the designs of the wings in the cocoon while the butterflies are still caterpillars. So taking it out of commission leaves the wings without a blueprint during their development.

If WntA lays down the lines for the wings, then the gene "optix" is the paint brush that fills them in, reports Nicholas Wade for the New York Times. In another study, researchers demonstrated in several species that disabling the gene caused many wing colors to disappear, writes Lallensack. Researchers are planning to study both genes further to see how they evolved to come to their current purposes in different species of  butterflies.

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Ben Panko is a staff writer for Smithsonian.com