Researchers report in PNAS how a single genetic switch controls mimicry in the swallowtail Papilio alphenor. Many butterflies use mimicry to resemble toxic species and avoid predators; this study explains how one locus can produce distinct wing patterns in males and females despite almost the same genome.
The team focused on doublesex, a locus that in these swallowtails behaves like a supergene but acts alone to determine mimicry. Using genomic sequencing and experimental tools including CRISPR, they showed the supergene gained a new role when it became linked to additional regulatory elements that change how the gene is expressed.
Surprisingly, the two alleles had few protein differences. Instead, the new allele acquired six cis‑regulatory elements in nearby non‑coding DNA. Those elements depended on the doublesex protein and together altered gene activation to produce the mimetic female pattern, in which females add orange spots to white patches while males retain standard white patches on a black background. The allele also regulated downstream genes involved in body plan development and wing patterning. Lead author Nicholas VanKuren (University of Chicago) noted where to look in genomes for colour switches, and senior author Marcus Kronforst highlighted how butterfly diversity makes them a good system to study the origin of new forms. The study was supported by the National Institutes of Health and reported by the University of Chicago; the post appeared on Futurity.
Difficult words
- locus — specific place on a chromosome or gene position
- mimicry — copying another species' appearance to avoid predators
- allele — one version of a gene at a single locusalleles
- supergene — group of linked genes acting together
- regulatory — controlling how genes are turned on
- express — produce or show a gene's effect in cellsexpressed
- downstream — acting later in a biological pathway
- genome — complete set of an organism's DNAgenomes
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Discussion questions
- How might finding a single genetic switch change future research on animal colour patterns or evolution?
- Why do the authors say butterflies are a good system to study the origin of new forms? Give two reasons based on the article.
- What are possible benefits and risks of using tools like CRISPR in studies of wild species?
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