The ‘Selfish’ Force of R2d2 Awakens
In the journal Molecular Biology and Evolution , researchers report that the genetic element, responder to meiotic drive on chromosome 2 ( R2d2 ), rapidly transmitted itself across diverse mouse populations from around the world, despite impairing female fertility. This study is one of few to demonstrate that a “selfish” allele can reach genetic fixation within populations while weakening the reproductive fitness of that species.
“The most striking thing is that R2d2 appears to violate Darwin’s fundamental principle of natural selection , which states that alleles that are beneficial for an organism’s reproductive fitness—its ability to survive and reproduce—should rise in frequency, while detrimental alleles should become rare,” said Andrew Morgan from the University of North Carolina , co-first author of the study. “ R2d2 has spread in a way that we expect of an advantageous allele, but actually it’s the opposite.”
Mendel’s first law grants genes or chromosomes a 50–50 shot of being passed on to offspring, enabling genetic diversity. However, R2d2 cheats natural selection by subverting meiosis, segregating its copies to the egg more than half of the time through a process called meiotic drive.
“With meiotic drive, the allele enhances its own transmission, so R2d2 promotes its spread to offspring at the expense of other alleles,” explained Morgan. “Our question was whether the driving allele at R2d2 could sweep to fixation in different populations of mice.”
The team studied R2d2 inheritance patterns in both lab and wild mouse populations taken from 15 countries. In laboratory mice, litter sizes decreased by 20% as a result of the meiotic drive. Meanwhile, the proportion of mouse chromosomes with R2d2 also increased rapidly in frequency, tripling in one laboratory population from 18% to 62% within 13 generations.
“The pace of the sweeps of R2d2 were surprising in the lab…even strong natural selection can take hundreds of generations to produce an appreciable change in allele frequency,” said Morgan.
The team is now studying the evolution of R2d2 as well as the mechanism behind its meiotic drive. “It is still hard to know how common ‘selfish sweeps’ are in nature,” said Morgan. “ R2d2 may still teach us more about both evolution and about the fundamental biology of chromosomes.”
Tags
Who is online
91 visitors
Amazing; yet, there is still so much yet to learn!
I'm confused. You surely don't mean THIS r2d2, right? I'm not trying to be obtuse, I promise... It's just confusing!