Why Deadly Mutations Persist

Duke researchers find a surprising genetic source of lethal mutations in fruit flies, with possible implications for conservation and health

Close up of fruit fly seen through a microscope.

This is a summary of a press release that originally appeared on Trinity College of Arts & Sciences.

Scientists have puzzled for decades over a basic evolutionary question: If lethal mutations are so deadly, why do these harmful bits of genetic code persist and spread through generations?

Sarah Marion began exploring the mystery as a Duke biology graduate student. “Almost every individual of any species studied has at least one lethal mutation,” Marion said. “I thought, how is that possible? Wouldn’t natural selection remove that?”

Marion is the lead author of a new study suggesting the answer lies not in tiny DNA errors as previously thought, but in mobile pieces of DNA known as transposable elements, also called transposons or “jumping genes.” These pieces of genetic code insert themselves into a genome, like some viruses. This creates bursts of mutations, temporarily outpacing natural selection’s ability to remove them.

To explore the dynamics of mutations, the team collected wild fruit flies using baited traps and identified about 300 fly lineages carrying lethal mutations. Over five years, researchers tracked those mutations across more than 21,000 fly pairings.

They expected to find tiny DNA glitches. Instead, the scientists discovered that most lethal mutations were triggered by transposable elements that had recently jumped into the species from another type of fruit fly.

“We’re seeing the same proportion of lethal mutations reported more than 50 years ago, but the genetic culprits are entirely different,” said Mohamed Noor, professor of biology and senior author. “They’re all recent invaders, revealing a hidden and fast-moving layer of evolution.”

The findings, published in PLOS Biology, could have implications for conservation. In small or endangered populations, these “genomic storms” can trigger rapid declines. Identifying these mechanisms could help scientists better monitor the genetic health of at-risk species and understand how genomes defend themselves against harmful DNA.

Transposable elements are also known to cause some diseases in humans, so a better understanding of their dynamics and evolution could have applications to human health.

To learn more, visit Trinity College of Arts & Sciences.