The DNA sequencing technology is helping scientists find answers to the questions that tormented people for centuries. Charting the genomes of animals, we get a better idea of how the giraffe acquired its long neck and why snakes are so long. Genome sequencing allows us to compare and contrast the DNA of different animals and figuring out how they evolved and to be who they are.
But sometimes we are faced with a mystery. The genomes of some animals, apparently, do not include certain genes that appear in other similar types and must be present to support the life of animals. These apparently absent genes, called "dark DNA". Her existence can turn our understanding of evolution.
For the first time, scientists led by Adam Harrison from the University of Oxford faced with this phenomenon during the sequencing of the genome sand rat (Psammomys obesus), a gerbil living in the desert. In particular, they wanted to study genes gerbils associated with the production of insulin, to understand why this animal is particularly susceptible to type II diabetes.
When they searched the Pdx1 gene that controls insulin secretion, they found that the missing along with the 87 other genes surrounding it. Some of these missing genes, including Pdx1, are vital, and without them, the animal can not survive. Where are they?
The first clue was the fact that in several body tissues sand rats, scientists found chemicals that could appear on the "instructions" of "missing" genes. This would be possible only if the genes present somewhere in the genome. And this would indicate that they are not missing, but simply disappeared.
The DNA sequence of these genes is very rich in guanine and cytosine, two of the four molecules of "bases" that make up DNA. We know that rich in cytosine and guanine sequences create problems for some methods of DNA sequencing. And it becomes more probable that the genes that we were looking for was on the spot, but they were difficult to detect. For this reason, we called this a hidden sequence of "dark DNA," as a reference to dark matter, which consists of 25% of the Universe, but we can't find it.
Studying the genome of the sand rats, we found that in one part, in particular, had a lot more mutations than other genes in rodents. All genes in this hotspot mutations were DNA rich in cytosine and guanine, and mutated to such a degree that they are difficult to detect using standard methods. Excessive mutation often stops the gene, but somehow the genes of the gerbils continue to play their roles, despite the radical change in DNA sequence. This is a very difficult task for the genes. It's like singing "Katyusha" using only vowels.
This kind of dark DNA previously found in birds. Scientists have discovered that gene 274 is "no" in the sequenced currently, the genomes of birds. Among them the gene for leptin (the hormone that regulates energy balance), which the scientist could not find for many years. Again, these genes have a very high content of cytosine and guanine and their products are found in the tissues of the bodies of birds, even if the genes themselves as it is not in geneticheskih sequences.
A ray of light in the dark DNA
In most of the textbooks meets the definition of, which implies that evolution proceeds in two stages: mutation, natural selection should. Mutation of DNA is a common and continuous process occurring completely by chance. Natural selection determines which mutations must pass, and which are not, usually depending on what result they showed in the process of reproduction. In short, the mutation creates the variation in the DNA of the organism, and natural selection decides to stay or drop out, and so is evolution.
But pockets of high mutations in the genome means that genes in certain places are more likely to mutate than others. This means that these lesions can be nedootsenennym mechanism that can also determine the course of evolution. And so estestvenny selection may not be the only driving force.
Still dark DNA, apparently, was present in two different and common types of Pets. But it is still unclear how she all spread. If the genomes of all animals contain DNA in the dark, and if not, what makes gerbils and birds so unique? The most addictive puzzle will be to figure out what the influence of dark DNA has had on the evolution of animals.
In the example with the sand rat, a hotbed of the mutation, may have led to the adaptation of animals to desert conditions. But, on the other hand, the mutation might have happened so fast that natural selection could not work fast enough to eliminate anything harmful to DNA. If so, then the deleterious mutations may interfere with the survival of the sand rat beyond its present desert environment.
The opening of this strange phenomenon certainly raises questions about how evolyutsioniruet genome, and that we might have missed in the current projects of genome sequencing. Maybe we should turn around and look closely.
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