Patterns, Genes, and Butterfly Wings

SCIENCE

Gene-hacking scientists reveal how a single gene helps determine the dizzying array of butterfly wing patterns. (Washington Post)

Take a look at the A-Z of butterfly wings.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit … and some gorgeous photos of butterflies. We couldn’t choose just one!

Photograph by Willard Culver, National Geographic

Discussion Ideas

Scientists recently edited the genes of butterfly wings. Let’s start with the easy part. What are butterfly wings? Read through this Nat Geo article for some help.
- Butterfly wings serve three big purposes: flight, camouflage, and sexual selection for mating.
  - Flight: Butterflies soar by using relatively big, light wings and slow wingbeats. Learn more here.
  - Camo: “Several butterflies use the patterns as warnings, like the orange and black of a monarch butterfly that tell predators they are poisonous. For some, such as the dead leaf butterfly, which looks like you might expect, wings are camouflage. Eyespots on wings fool predators into attacking from the rear rather than the head. Other bright butterflies communicate with sex symbols in scaly flashes.”
  - Sexual Selection: Male and female butterflies take turns courting—showing off their beautifully ornamented wings to attract a mate.

OK. What is gene-editing?
- Genome editing is a type of genetic engineering in which DNA is inserted, deleted or replaced in the genome of a living organism.
- To edit butterfly genomes, scientists used CRISPR, a naturally occurring series of DNA sequences in bacteria. CRISPR is a part of a gene-editing technique sometimes nicknamed “molecular scissors” for the way it can cut into strands of DNA.
  - Using CRISPR, scientists involved in the butterfly study deleted WntA (“wint-ay”), a signaling gene they knew was important in determining wing patterns.

Why are butterflies and butterfly wing patterns valuable in the study of genetics?
- Butterflies are valuable to scientists for their sheer diversity. There are more than 20,000 species of butterfly alive today, all descended from a single species of moth, and examples of most butterfly species are preserved as specimens in museums.
- Butterfly wing patterns are appealing “because, though they’re ornate, they exist on a simple canvas: Unlike the architecture of our hearts or brains, butterfly markings are confined to essentially two dimensions.”
  - The Washington Post article describes butterfly wings as “scales arrayed into patterns like ceramic tiles in a mosaic.”

“This study highlights how flexible [WntA gene regulation] is, to be involved in so many aspects of patterning. It’s extraordinary!” What do scientists mean by this? What did they discover about the influence of WntA on butterfly wings?
- First, they discovered that WntA turns on when butterflies are still caterpillars. Long before the animals even have wings, WntA is “already providing the spatial information necessary to make patterns.” (Spatial information! Geography is destiny.)
- WntA, a single gene, is responsible for a dazzling array of pattern elements: size, shape, location on the wing, color, and color intensity.
  - WntA and optix, another gene studied, are “paintbrush genes. Wherever you put them, you’ll have a pattern.”