At least three-quarters of the human genome consists of a non-functional “junk DNA,” say the results of a recent study by scientists. Since the discovery by Watson and Crick of the double helix DNA in 1953, the scientific community has been arguing about which part of the genome makes you you. And according to the evolutionary biologist Dan Graur from Houston University, the answer to this riddle is hidden in simple mathematical calculations.
Graur calculated that the functional part of the human genome is only 10 to 15 percent of our total DNA with an upper limit of about 25 percent. The rest of the genome – about 75-90% – is a so-called junk DNA, not necessarily a harmful but completely useless genetic code of distorted nucleotide sequences that do not possess any useful function, for example, encoding proteins that stimulate important chemical reactions within our Organisms.
The rationale for the Gaura model is based on how different mutations fall into the DNA strings and how we, as a species, have been able to take advantage of the benefits derived from these mutations. These genetic variations from time to time appear in our genome and slightly alter or rearrange the four chemical components that make up our DNA – adenine, cytosine, guanine and thymine – in various parts of it.
When mutations occur in garbage DNA, they are considered neutral, since this genetic code does not perform any function. However, when the mutation occurs in the functional DNA chain, it also happens that this mutation harms and in some cases may even be fatal to the body, as the code for healthy tissue and biological processes is rewritten.
Proceeding from this, it turns out that for our evolutionary prospects it is much better when fewer parts of DNA are functional, as in this case the risk of harmful mutations decreases and the probability of early death that these mutations can approximate decreases.
In the calculations of Graur, where, on the one hand, the risk of harmful mutations for species survival is taken into account, and on the other hand – the known indicator of population stability and the reproductive level throughout human history, the limit of functional DNA should always remain low. Otherwise, dangerous mutations would continue to accumulate and would have to reproduce an incredibly large number of new individuals to obtain only a small percentage of healthy cubs for survival.
“Assuming the 100% functionality of the genome and the speed with which harmful mutations spread, it turns out that to maintain a constant population size, each pair must produce a minimum of 24 children and a maximum of 5 × 10 ^ 53,” the author of the work reports.
Of course, hardly anyone except creationists believes that the human genome does not have junk DNA, but in a major study of 2012 for the Encyclopedia of DNA Element (ENCODE) project, researchers stated that about 80 percent of DNA is functional. Conclusions seemed very controversial. Partly because many scientists said that the definition of ENCODE for the term “functional” was too broad.
In the understanding of the term Grauer, where functional DNA is regarded as code, the development of which is useful from the point of view of evolutionary effects, a figure of 80 percent does not correspond to the result.
“If 80 percent of the genome functioned, each pair on the planet would need to give birth to an average of 15 children. However, only two of them could continue the genus. The rest either would die or not have reproductive functions, “the author writes.
According to Graur, it is likely that only about 10-25 percent are useful. At the same time, despite the fact that it is hardly possible to put an end to this field of research, new results to some extent coincide with the results of an independent study conducted in 2014. Then it was said that only 8.2% of our DNA is functional. It is possible that such statements will prompt other scientists to dig deeper into this issue.
“We need to know the volume of the functional part of the human genome in order to focus on what is really important in research. And already on this basis, create medicines that can treat and prevent diseases, “Graur said.
“There is no need to study everything in a row. We need to know only those parts of DNA that are functional. ”
The results of Graura’s study were published by the scientific publication Genome Biology and Evolution.