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Scientists can now alter butterfly wing patterns

Using a technique known as gene knockout, researchers altered the genetic code in the DNA of seven species of butterflies. This led to a breakthrough discovery that a single gene, the WntA gene, is responsible for the incredible diversity of butterfly wing patterns.

Owen McMillan is a staff scientist at the Smithsonian Tropical Research Institute and co-author of the study.

“Butterfly wing patterns are amazing: a true evolutionary novelty, highly diverse and strongly shaped by natural and sexual selection,” said McMillan. “By genetically engineering individuals from different species, we are quickly coming to grips with how this diversity is generated. Surprisingly, a single gene, and one that is used repeatedly throughout development, can have huge effects.”

The WntA gene is part of a small family of genes that influence body plans and other patterns during insect development. WntA is a protein molecule that seems to act as a morphogen, a chemical agent that is capable of causing the development of morphological characteristics.

“Imagine a paint-by-number image of a butterfly,” said McMillan “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 two’s red’ or ‘paint the number one’s black. Of course, it is a lot more complicated than this because what is actually changing are networks of genes that have a cascading effect on pattern and color.”

According to researcher Carolina Concha, the team injected butterfly eggs with an RNA probe that attached to the WntA gene, which they suspected played some role in the expression of color.

“After knocking out the gene, we let the butterflies grow up and compared the wing patterns of the knockout mutants with the original wing patterns,” said co-author Richard Wallbank.

The scientists repeated this same procedure in seven different butterfly species. The results of the study revealed that the WntA gene influences wing pattern in ways that the researchers had not expected.

“Going back to the paint-by-number analogy, ‘Number one’ can move around the wing in different butterflies species, and even in different color pattern variants of the same species,” said McMillan. “In Monarchs, for example, the gene is expressed with fine precision along the wing veins. In contrast, in Heliconius, a group known for vivid wing patterns, the gene is expressed in bold brush strokes from essentially the tip to the base of the wing.”

McMillan added, “And it gets even crazier, because the color of ‘Number one’ can change depending on context, shifting between different colored pigments and even changing how light is reflected. In butterflies, color is a function of both pigment and the structural properties of the scales cells that cover the wing.”

The research is published in the Proceedings of the National Academy of Sciences early online edition.

By Chrissy Sexton, Staff Writer

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