Within a single species of butterfly, many different wing patterns may appear. How is it possible? According to researchers Ben Wielstra and Emma Berdan from the Leiden Institute of Biology (IBL), the answer lies in supergenes. A supergene is a part of a chromosome that contains many closely linked genes. Together, these genes form the basis of complex traits in plants and animals.
“The idea of supergenes is relatively old. Only now, with today’s modern DNA techniques, can we map them correctly. Recently it has become clear that supergenes are much more common than previously thought,” says Wielstra. On June 13, Wielstra and postdoc Emma Berdan will publish a special issue on supergenes in the scientific journal Philosophical Transactions of the Royal Society B.
What are supergenes?
“Supergenes are parts of chromosomes that contain multiple genes that are inherited as a whole,” says Wielstra. What makes supergenes remarkable is the lack of recombination. Recombination is the mixing of genetic information from two parents so that the offspring receives a unique set of chromosomes. “Because there is no recombination in supergenes, all the genes they contain evolve together as a single unit. This allows different versions of supergenes to appear within a species, resulting in major differences in appearance and behavior.
Supergenes can appear in different ways. “There are areas of the genome where recombination naturally occurs less frequently. At the same time, recombination can also be stopped when, for example, the structure of the genome changes. A well-known example of this is an inversion. Part of the chromosome breaks off and is reversed so that the order of the genes no longer matches the original. Recombination is then no longer possible.
The collar as an example
The presence of supergenes leads to more variation within a species. “My favorite example is the strawberry. In these birds, supergenes ensure that males have dark or white feathers around their heads. There are also males that do not develop a feather collar at all and look like females. These three types of male ruffs not only differ from each other in appearance, but they also behave differently during mating season,” says Wielstra.
Does it provide an evolutionary advantage?
‘Sometimes. On the one hand, variation within a species is useful. This allows species to switch between different survival strategies,” says Wielstra. According to him, supergenes can facilitate this process. But not without price. “Without recombination, harmful mutations can quickly accumulate.” In the crested newt, which Wielstra and Berdan studied, the accumulation of mutations in a supergene rendered half of the salamander eggs nonviable. Wielstra: “This supergene can be considered an extreme example of an inherited disease. »
“Supergenes Are Hot”
By studying the evolution of supergenes, researchers hope to better understand the origin of hereditary diseases. In people too. “Supergenes are hot. More research is being done on this topic than ever before. As a result, we continue to find more and more examples where large differences in behavior and appearance are influenced by a single supergene. With the special issue on supergenes, Wielstra and Berdan hope to give a good overview of the current state of research in this area.Wielstra: “We now know that supergenes are common. The next step is to find out exactly how they arise .
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