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Supergenes can complicate the mating process. In some species, supergenes create a reproductive system that has practically four sexes. In North American birds, due to a supergene called white-throated sparrows, for example, there are two “morphs” with similar colors and characteristics. Males need to find a partner from the opposite morph, not just females. Otherwise, the offspring will die inheriting the supergene from both parents or inheriting none at all. Only chicks inherit a “balanced killer” of one supergene and one normal chromosome segment.
At such a high price, it’s a wonder superjeans were invented at all, says Berdan. “Any kind of variation would be very difficult to maintain, especially over millions of generations,” she said. “This is one of the great secrets of supergenes.” She suggests that multiple types of selection may be working together to maintain supergenes, and that some areas may be more favorable for their persistence in the population.
Interestingly, one of the mechanisms for sometimes maintaining supergenes appears to be recombination—a phenomenon they normally oppose. Amanda Larraquente, an evolutionary geneticist at the University of Rochester, and her collaborators last April. eLife.
Laraquente was not interested in the original supergenes or their evolutionary costs. Her focus was on selfish genes, segments of DNA that spread in a population without benefiting their hosts. She is possessed by a selfish gene. separation disorder (SD) raised in certain fruit flies in Zambia. “It’s a sperm killer,” she explains, “but it only kills the chromosomes it contains.” SD.
Sometime in the last 3,000 years, a version SD A large piece of chromosomal DNA is trapped and known as a supergene SD-Evil It has spread to fruit fly populations throughout Africa. “It’s really the selfish gene,” Laraquente said.
DNA Sequencing and Analysis Chromosome by Laraquente, Devon Presgrees and colleagues SD-Evil The lack of integration between them accumulates harmful mutations, as fully predicted SD-Evil and its sister chromosome. But the researchers did not find as many mutations as they had hoped.
The reason is that sometimes flies inherit two chromosomes SD-Evil– and the two supergenes are similar enough to allow some recombination between them. That recombination eventually purges a few deleterious mutations from the flies’ supergenes.
“As it turns out, just a little re-mixing is enough,” Larracuente said. She and Presgraves are now looking for another SD Supergenes in wild fruit are screened in populations for clues to evolution and supergene effects.
Their results show that the purifying effect of recombination on the genome never ceases to be important. Stable and predictable supergene inheritance of complex traits can be useful in helping species adapt, but even supergenes can benefit from mixing things up once in a while.
Original story Reprinted with permission Quanta Magazine, Editorially independent publication Simons Foundation Its mission is to advance public understanding of science by covering research developments and trends in the mathematical and physical and life sciences.
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