MUTATIONS in the DNA of voles found in the “hot zone” around the devastated Chernobyl nuclear plant are cropping up at a far higher rate than expected. Results of research on the voles, presented at the annual meeting of the Society for the Study of Evolution in Montreal last month, raises questions about the full effect of radiation on animal populations and on humans.
American researchers led by Ron Chesser of the University of Georgia’s Savannah River Ecology Laboratory examined the DNA in mitochondria, the energy-producing bodies in the cell cytoplasm. They found 46 mutations in just one gene, the cytochrome b gene, in nine voles taken from the 30-kilometre restricted zone around Chernobyl. When they examined 10 animals from outside the “hot zone”, they found four mutations.
Chesser says he was surprised by the sheer number of mutations. There are “many more mistakes than what was thought to be feasible in a thriving population”, he says. The study raises questions for geneticists about how many mutations a population can tolerate without dying off, he says.
The results also have implications for humans. The Atomic Bomb Casualty Commission spent years looking for any kind of genetic damage in the survivors of the Hiroshima and Nagasaki bombs, says Christopher Wills, an evolutionary geneticist at the University of California in San Diego. They did not report much beyond stillbirths and some cases of cancer, he says. James Crow, a member of the commission’s advisory committee says he has no doubt that genetic changes were induced by the radiation from the bomb “but they were below the threshold of detection”. The new data may help researchers to home in on changes in people exposed to radiation at Chernobyl.
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Researchers cannot agree on the natural background rate at which mutations appear in mitochondrial DNA. But even choosing a conservative rate – of, say, 1 in 100 000 per gene per generation – the voles from the contaminated zone have a mutation rate about 40 times that of the background rate, says Chesser. The rate was found to be high enough to cause mutations from one generation to the next.
The team is looking at other genes in mitochondria and in the nucleus to see if the effects are widespread. It would be strange, says Chesser, “for us to have stumbled upon the only gene showing this kind of alteration”.
![Astronomers have long known that understanding how star clusters come to be is key to unlocking other secrets of galactic evolution. Stars form in clusters, created when clouds of gas collapse under gravity. As more and more stars are born in a collapsing cloud, strong stellar winds, harsh ultraviolet radiation and the supernova explosions of massive stars eventually disperse the cloud, and their light can bear down on other star-forming regions in the galaxy. This process is called stellar feedback, and it means that most of the gas in a galaxy never gets used for star formation. Researching how star clusters develop can answer questions about star formation at a galactic scale. Now, the state of the art has been further developed with both Hubble and Webb working together to provide a broad-spectrum view of thousands of young star clusters. An international team of astronomers has pored over images of four nearby galaxies from the FEAST observing programme (#1783), trying to solve this mystery. Their results show that it is the most massive star clusters that clear away their gaseous shroud the fastest, and begin lighting their galaxy the earliest. The team identified nearly 9000 star clusters in the four galaxies in different evolutionary stages: young clusters just starting to emerge from their natal clouds of gas, clusters that had partially dispersed the gas (both from Webb images), and fully unobstructed clusters visible in optical light (found in Hubble images). With Webb???s ability to peer inside the gas clouds, they were able to then estimate the mass and age of each cluster from its light spectrum. This image shows a section of one of the spiral arms of Messier 51 (M51), one of the four galaxies studied in this work, as seen by Webb???s Near-Infrared Camera (NIRCam). The thick clumps of star-forming gas are shown here in red and orange, representing infrared light emitted by ionised gas, dust grains, and complex molecules such as polycyclic aromatic hydrocarbons (PAHs). Within these gas complexes, each tens or hundreds of light years across, Webb reveals the dense, extremely bright clusters of massive stars that have just recently formed. The countless stars strewn across the arm of the galaxy, many of which would be invisible to our eyes behind layers of dust, are also laid bare in infrared light. [Image description: A large, long portion of one of the spiral arms in galaxy M51. Red-orange, clumpy filaments of gas and dust that stretch in a chain from left to right comprise the arm. Shining cyan bubbles light up parts of the gas clouds from within, and gaps expose bright star clusters in these bubbles as glowing white dots. The whole image is dotted with small stars. A faint blue glow around the arm colours the otherwise dark background.]](https://images.newscientist.com/wp-content/uploads/2026/05/13114322/SEI_296271016.jpg)
