Shedding Light on Dark DNA
Most textbook definitions of evolution state that it occurs in two stages: mutation followed by natural selection. DNA mutation is a common and continuous process, and occurs completely at random. Natural selection then acts to determine whether mutations are kept and passed on or not, usually depending on whether they result in higher reproductive success. In short, mutation creates the variation in an organism’s DNA, natural selection decides whether it stays or if it goes, and so biases the direction of evolution.But hotspots of high mutation within a genome mean genes in certain locations have a higher chance of mutating than others. This means that such hotspots could be an underappreciated mechanism that could also bias the direction of evolution, meaning natural selection may not be the sole driving force.So far, dark DNA seems to be present in two very diverse and distinct types of animal. But it’s still not clear how widespread it could be. Could all animal genomes contain dark DNA and, if not, what makes gerbils and birds so unique? The most exciting puzzle to solve will be working out what effect dark DNA has had on animal evolution.In the example of the sand rat, the mutation hotspot may have made the animal’s adaptation to desert life possible. But on the other hand, the mutation may have occurred so quickly that natural selection hasn’t been able to act fast enough to remove anything detrimental in the DNA. If true, this would mean that the detrimental mutations could prevent the sand rat from surviving outside its current desert environment.The discovery of such a weird phenomenon certainly raises questions about how genomes evolve, and what could have been missed from existing genome sequencing projects. Perhaps we need to go back and take a closer look.
This article was provided by The Conversation. Materials may have been edited for clarity and brevity.