News | Study reveals how ‘selfish chromosomes’ hijack genetic mechanisms to eliminate competing sperm
A new study led by the University of Utah has revealed a genetic mechanism that has long puzzled evolutionary biologists: how “selfish chromosomes” manipulate reproduction to increase their chances of being passed to the next generation. The study found that these chromosomes hijack a gene called Overdrive (Ovd) to eliminate competing sperm.
Normally, Overdrive provides “quality control” during sperm development by identifying and removing abnormal sperm cells. Selfish chromosomes exploit this mechanism to eliminate healthy competitors and improve their own odds of inheritance.
The findings were published in Nature Communications.
Segregation distortion breaks the 50% inheritance rule
Under Mendelian inheritance, parental genes generally have about a 50% chance of being passed to offspring. In some cases, however, genes use special mechanisms to improve their odds of inheritance.
This phenomenon is known as segregation distortion.
The team observed it in two fruit fly species. Although the species carry entirely different selfish chromosomes, both exploit the same genetic pathway—Overdrive.
First author and University of Utah biologist Jackson Ridges said this was the first finding that independently evolved selfish chromosomes rely on the same gene to eliminate competing gametes.
He said, “This is the first demonstration that the same gene plays a key role in multiple independent selfish chromosome systems. It suggests that different chromosomes may evolve independently while exploiting the same cellular mechanism.”
Overdrive normally removes abnormal sperm
Researchers found that Overdrive normally functions like a quality-control system during sperm development.
If abnormalities arise during sperm formation, Ovd triggers a mechanism that prevents those gametes from continuing to develop, helping maintain germ-cell quality.
Selfish chromosomes can manipulate this mechanism so that it removes not only abnormal sperm but also normal sperm carrying other chromosomes.
This gives sperm carrying the selfish chromosome a competitive advantage and makes the chromosome more likely to reach the next generation.
Gene knockout experiments reveal its key role
To test Ovd's role, the team performed gene knockout experiments in Drosophila pseudoobscura and Drosophila melanogaster.
They deleted Ovd and observed the effects on reproduction. Surprisingly, the flies still produced sperm largely normally without the gene.
This suggests that Ovd is not essential for sperm formation and instead likely performs quality control.
The researchers compared this mechanism with the well-known tumor suppressor gene P53. P53 normally prevents excessive cell proliferation, but in the absence of DNA damage, cells can survive without it.
The team therefore hypothesized that Ovd may act only when it detects an abnormality.
Heat experiment confirms quality-control function
To test this hypothesis, researchers used a known phenomenon in fruit fly reproduction: male flies generally become infertile above 31°C, although the reason has been unclear.
Normal flies and flies lacking Ovd were kept at high temperature for one week.
Normal flies became completely infertile, while flies lacking Ovd still produced offspring.
The team inferred that under stress such as high temperature, Ovd prevents potentially damaged sperm from developing and thereby avoids the production of poor-quality gametes.
Co-author and University of Utah associate professor Nitin Phadnis said, “This result makes it nearly certain that Overdrive's normal function is to prevent the production of abnormal gametes. When we remove this ‘blocker,’ the behavior of selfish chromosomes also disappears.”
Researchers emphasized that Overdrive is not itself a “selfish gene,” but a reproductive quality-control system exploited by selfish chromosomes.
Potential clues to infertility and species evolution
Scientists first discovered segregation distortion in the fruit fly Drosophila obscura in the 1920s. Similar mechanisms have since been found throughout the animal kingdom, from nematodes to mammals, but their molecular basis has remained unclear.
Although no identical genetic system has been identified in humans, researchers believe humans may have similar reproductive quality-control mechanisms involving different molecular tools.
The team said the discovery may offer new clues to the genetic mechanisms of male infertility and reproductive isolation between species.
Phadnis noted that scientists have long sought to explain how selfish genes cause infertility and drive speciation, and deeper study of Overdrive offers a new direction.
Future studies will explore similar mechanisms in more species
The team plans to knock out Overdrive in more fruit fly species to assess whether other selfish chromosomes also exploit this quality-control system.
Researchers also plan to investigate whether similar segregation distortion exists in the human lineage.
They said a deeper understanding of this genetic “internal competition” may reveal genetic conflict in evolution and advance reproductive biology and genetics.
Story source:
Collected online
Published 2026-03-16
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News | Study reveals how ‘selfish chromosomes’ hijack genetic mechanisms to eliminate competing sperm
News | Study reveals how ‘selfish chromosomes’ hijack genetic mechanisms to eliminate competing sperm
A new study led by the University of Utah has revealed a genetic mechanism that has long puzzled evolutionary biologists: how “selfish chromosomes” manipulate reproduction to increase their chances of being passed to the next generation. The study found that these chromosomes hijack a gene called Overdrive (Ovd) to eliminate competing sperm.
Normally, Overdrive provides “quality control” during sperm development by identifying and removing abnormal sperm cells. Selfish chromosomes exploit this mechanism to eliminate healthy competitors and improve their own odds of inheritance.
The findings were published in Nature Communications.
Segregation distortion breaks the 50% inheritance rule
Under Mendelian inheritance, parental genes generally have about a 50% chance of being passed to offspring. In some cases, however, genes use special mechanisms to improve their odds of inheritance.
This phenomenon is known as segregation distortion.
The team observed it in two fruit fly species. Although the species carry entirely different selfish chromosomes, both exploit the same genetic pathway—Overdrive.
First author and University of Utah biologist Jackson Ridges said this was the first finding that independently evolved selfish chromosomes rely on the same gene to eliminate competing gametes.
He said, “This is the first demonstration that the same gene plays a key role in multiple independent selfish chromosome systems. It suggests that different chromosomes may evolve independently while exploiting the same cellular mechanism.”
Overdrive normally removes abnormal sperm
Researchers found that Overdrive normally functions like a quality-control system during sperm development.
If abnormalities arise during sperm formation, Ovd triggers a mechanism that prevents those gametes from continuing to develop, helping maintain germ-cell quality.
Selfish chromosomes can manipulate this mechanism so that it removes not only abnormal sperm but also normal sperm carrying other chromosomes.
This gives sperm carrying the selfish chromosome a competitive advantage and makes the chromosome more likely to reach the next generation.
Gene knockout experiments reveal its key role
To test Ovd's role, the team performed gene knockout experiments in Drosophila pseudoobscura and Drosophila melanogaster.
They deleted Ovd and observed the effects on reproduction. Surprisingly, the flies still produced sperm largely normally without the gene.
This suggests that Ovd is not essential for sperm formation and instead likely performs quality control.
The researchers compared this mechanism with the well-known tumor suppressor gene P53. P53 normally prevents excessive cell proliferation, but in the absence of DNA damage, cells can survive without it.
The team therefore hypothesized that Ovd may act only when it detects an abnormality.
Heat experiment confirms quality-control function
To test this hypothesis, researchers used a known phenomenon in fruit fly reproduction: male flies generally become infertile above 31°C, although the reason has been unclear.
Normal flies and flies lacking Ovd were kept at high temperature for one week.
Normal flies became completely infertile, while flies lacking Ovd still produced offspring.
The team inferred that under stress such as high temperature, Ovd prevents potentially damaged sperm from developing and thereby avoids the production of poor-quality gametes.
Co-author and University of Utah associate professor Nitin Phadnis said, “This result makes it nearly certain that Overdrive's normal function is to prevent the production of abnormal gametes. When we remove this ‘blocker,’ the behavior of selfish chromosomes also disappears.”
Researchers emphasized that Overdrive is not itself a “selfish gene,” but a reproductive quality-control system exploited by selfish chromosomes.
Potential clues to infertility and species evolution
Scientists first discovered segregation distortion in the fruit fly Drosophila obscura in the 1920s. Similar mechanisms have since been found throughout the animal kingdom, from nematodes to mammals, but their molecular basis has remained unclear.
Although no identical genetic system has been identified in humans, researchers believe humans may have similar reproductive quality-control mechanisms involving different molecular tools.
The team said the discovery may offer new clues to the genetic mechanisms of male infertility and reproductive isolation between species.
Phadnis noted that scientists have long sought to explain how selfish genes cause infertility and drive speciation, and deeper study of Overdrive offers a new direction.
Future studies will explore similar mechanisms in more species
The team plans to knock out Overdrive in more fruit fly species to assess whether other selfish chromosomes also exploit this quality-control system.
Researchers also plan to investigate whether similar segregation distortion exists in the human lineage.
They said a deeper understanding of this genetic “internal competition” may reveal genetic conflict in evolution and advance reproductive biology and genetics.
Story source:
Collected online