Genome complexity: role of supergenes (Introduction)

by David Turell , Tuesday, November 08, 2022, 22:28 (526 days ago) @ David Turell

A new developing field of study:

https://www.quantamagazine.org/how-supergenes-fuel-evolution-despite-harmful-mutations-...

"Birds and other predators avoid Heliconius butterflies because they are toxic to eat, with a bitter taste. The mimics were not toxic, but because they looked so much like the foul-tasting Heliconius, they were less likely to be eaten. The closer the resemblance, the more potent the protection.

"What Bates and many later evolutionary biologists couldn’t explain was how this mimicry was possible.

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"Today we know that in many species the answer is supergenes — stretches of DNA that lock several genes together into a single inheritable unit. “They’re kind of a wild card,” said Marte Sodeland, a molecular ecologist at the University of Agder in Norway. This aggregated form of inheritance “has obvious advantages, because it allows rapid adaptation, but there’s a lot we don’t know yet.”

"Supergenes once seemed like an evolutionary oddity, but the rise of genetic sequencing has shown that they are far more common than researchers believed. Not all supergenes may serve a function, but work in just the past few years has revealed that traits in a wide range of animal and plant species might be driven by these groups of genes that function like a single gene.

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"Supergenes seem to hold explanations for many long-standing mysteries of evolution, such as how species can sometimes adapt to new environments rapidly, how populations can sometimes evolve in different directions even while living close together, and why some species have “balanced lethal systems” of breeding, such that they must have two different versions of a chromosome to survive.

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"But supergenes aren’t all-powerful. Recent work on the evolution of supergenes is painting a nuanced picture of their effects. These theoretical models and studies of real populations have shown that supergenes often accumulate harmful mutations far more rapidly than other pieces of DNA do, and this can gradually lead to degenerative effects that undermine the original benefits.

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"But supergenes aren’t all-powerful. Recent work on the evolution of supergenes is painting a nuanced picture of their effects. These theoretical models and studies of real populations have shown that supergenes often accumulate harmful mutations far more rapidly than other pieces of DNA do, and this can gradually lead to degenerative effects that undermine the original benefits.

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"...researchers have been probing how supergenes arise and what the consequences for species might be as their supergenes continue to evolve. Understanding the origin of a supergene is “one of the most challenging questions,” said Tanja Slotte , an evolutionary geneticist at Stockholm University who studies supergenes in plants. “And it’s not a given that it’s even always possible.”

"In one recent effort, Katie Lotterhos, an evolutionary marine biologist at Northeastern University, built a computer model to study the first tentative steps taken on the path from inversion to supergene. Her model, published in the Philosophical Transactions of the Royal Society B in August as part of a special issue on supergenes, showed that the larger the initial DNA flip-flop, the more likely a supergene was to evolve. The reason was simple: A larger inverted fragment of DNA was more likely to capture multiple genes and lock them together as a single entity. Any beneficial mutations arising within the inversion could then promote its spread as a supergene.

"But the more important insight from Lotterhos’ model was that inversions themselves do not necessarily provide an evolutionary advantage. If a suite of genes is already well adapted to its surroundings, locking it into an inversion will not suddenly allow it to take off as a supergene. That fact may help to explain why complex vital traits aren’t routinely secured as supergenes: Ordinary selection pressures are often sufficient to preserve the traits.

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"For supergenes, however, that isn’t true. Since they rarely recombine, any harmful mutations they acquire tend to stay in place. The benefits of supergenes, then, could be accompanied by significant disadvantages."

Comment: presented to reveal a whole new area of genome research.