Biologist spoke about the prospects for 100% DNA disclosure
The human genome is 100 percent decrypted. An international team of scientists reported this in the journal ZME Science. If earlier geneticists did not have a complete idea of the sequence of all nucleotides (8% of the unread text remained), now they have also been deciphered. Everything is due to the new decoding technology, in which DNA is not cut into separate small pieces, but is examined as a whole passing through the nanopore. We asked to tell you about the prospects in the study of the genome that this achievement opens up. Head of the Laboratory of the Institute of General Genetics named after N.I. Vavilov RAS, Doctor of Biological Sciences, Professor Sergei KISELEV.
– Sergey Lvovich, please explain what exactly helped to “read” the full genome?
– Previous technologies for reading genetic text were based on the processing of short “words” (chunks of the genome). They took separate such words, which consisted of, say, 50-200 “letters” (nucleotides), and read them at first in a chaotic order, and then, using a computer, they performed bioinformatic analysis, looked for overlapping fragments at the ends and built them into a long full text …
But the process of reading was complicated by repetitive sequences. They have the genome not only of humans, but also of all other animals. What it is? This, for example, when the genetic “word” (they are written using the four letters G, A, T and C), consists only of the letter “A”. Imagine a thousand letters “A” or a combination of thousands of “TA”.
– What are these repetitions connected with?
– With the functioning of the genome. There is an assumption that they are a kind of his reserve. For example, such repetitive sequences are known to be found at the ends of each chromosome. And since it is known that the chromosome shortens with each cell division, it turns out that the repeats at its ends perform a protective function against rapid shortening with age.
The second function of repeating elements may be related to cell division. The scientists were led to this idea by the fact that repeats were also found in the central regions of chromosomes – centromeres, “knots” of which paired chromosomes are connected and to which protein filaments are attached, stretching the chromosomes in two directions during cell division.
Sometimes repetitions tell geneticists about a person’s predisposition to a particular ailment. This has been well studied using the example of age-related neurodegenerative diseases. By the number of repetitions in a particular gene, experts judge the likelihood of the development of the disease in the future. For example, with an existing propensity for Gensington’s disease, up to 34 repetitions are considered normal. But if there are, for example, 40 of them, then there is a high probability that the disease will manifest itself by the age of 40. And if a child has 100 repetitions after birth, then with a 100 percent probability we can say that he will develop Gensington’s disease at the age of 10 or earlier.
But back to decoding the genome. With the previous method (by cutting DNA into small fragments), geneticists could be mistaken in determining the length of the above-described repeats. And three years ago, a new technology for reading a genetic text was invented. It made it possible to read very long sequences of hundreds of thousands, millions of letters located in the DNA chain. This technology made it possible to read the remaining 8% of the genome, which were represented by just repeating elements. She made it possible to understand what extent they actually have and where exactly they are in the genome.
– The researchers said they studied 3.055 billion base pairs of the human genome. How can you imagine them?
– These are the very letters, nucleotides that make up the text of our genome. There are 3,055 billion of them in each of our cells. In terms of capacity, each can be compared with a 3 megabyte flash drive. And there are 10 such flash drives in our body to the 14th power!
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