MOSCOW, May 12, Vladislav Strekopytov. Members of the international consortium Zoonomia announced the completion of a 20-year project. Biologists deciphered the genomes of 240 animals from various families and compared them with the human DNA sequence. The results allowed us to better understand at what stage of evolution the changes that made us human took place.
Zoonomia Project
The term «zoonomy» was introduced into scientific use by Erasmus Darwin, an outstanding English physician and biologist, grandfather of Charles Darwin. In the book «Zoonomy, or the laws of organic life», published in 1794, he expressed a bold idea for his time: he suggested that all warm-blooded animals are related to each other and had a common ancestor in the distant past.
Two centuries later, the scientist's ideas received brilliant confirmation. In the early 2000s, the complete genomes of mice, humans, rats, and chimpanzees were published and found to be very close. More data were needed to understand at what point the evolutionary lines diverged.
As part of the Zoonomia project, biologists have deciphered and compared the genomes of 241 species of mammals, including humans. DNA samples were provided by over 50 scientific organizations from different countries. The results of the study were released in the form of 11 articles in the thematic issue of the journal Science.
According to biologists, there are more than 6,500 modern species of mammals and about 20,000 extinct ones. Despite the anatomical similarity, they are very different in appearance — from a tiny pygmy polydent, weighing less than two grams, to huge whales. Some are covered with a thick six, others are practically bald, someone has learned to fly, someone has adapted to life in the water, someone has an extremely sensitive nose, and someone, like a person, has a large and complex brain.
The objective of the Zoonomia project was to identify the DNA features that determine species differences, and to determine at what stage in evolutionary history they were fixed at the genetic level. The studies concerned only representatives of the plantental group, which appeared on the planet over the past 100 million years, and did not affect the more ancient marsupials and oviparous.
The method of comparative genetics used by scientists made it possible to identify< /u> genomic regions responsible for such characteristic traits as a keen sense of smell, the habit of hibernating, the ability to make sounds, brain development.
By tracing the history of individual genes, experts established that the diversity of mammals began to grow long before the extinction of dinosaurs, which occurred 66 million years ago, at the turn of the Cretaceous and Paleogene periods. Previously, it was believed that mammals mastered all ecological niches only after the extinction of dinosaurs.
How many animals are there in us
Chromosomes enclosed in a human cell contain about 20,000 genes encoding proteins. Together, this is no more than 1.5 percent of the total genetic material. In addition to them, the genome has many sequences responsible for the regulation — control of gene expression. It is much more difficult to identify the functions of such regulatory elements than the genes responsible for the production of specific proteins.
press releasewords of Elinor Karlsson, co-leader of the Zoonomia project, director of the Vertebrate Genomics Group at the Broad Institute of the Massachusetts Institute of Technology and Harvard. “The results show that we can understand a lot by studying the genomes of other mammals.”
The comparison method allowed researchers to identify more than three million regulatory elements in human DNA, about half of which were previously unknown. It turned out that there are at least ten times more of them than those that code for proteins, and they play a crucial role in controlling all physiological processes in the body, since they contain instructions for determining where, when and how much to produce proteins.
It also turned out that about 11 percent of the genome — about 4,500 regions in total — are identical in all mammals, including humans. These are the so-called conservative DNA fragments that remain unchanged for millions of years and are responsible for the features that distinguish mammals from other organisms. About four percent were classified by scientists as «highly conserved», apparently responsible for the most basic molecular processes at the cellular level, inherent in all eukaryotes.
Conservative DNA regions are necessary for the normal functioning of the body, and genetic changes in them can become causenot only hereditary diseases, but also cancer. Scientists give the example of a patient with medulloblastoma, in whom the rapid growth of a brain tumor was associated with a mutation in one of these regions of the genome.
Brain evolution catalyst
In the early 2000s, biologists discovered regions in the human genome associated with brain development. They were called «zones of accelerated human development» (HAR — Human Accelerated Regions). Some of them play an important role in the formation of neural pathways associated with intelligence in the embryonic stage.
Geneticists studying HAR in the Zoonomia project found that others have similar sites primates. But in the human genome, they contain genes that are different from our closest relatives, like chimpanzees and bonobos. Differences arose about a million years ago. In this case, we are not talking about the appearance of some special «gene of consciousness», but only about the restructuring of the protein packaging of DNA.
“Imagine the DNA of our last common ancestor with chimpanzees as a scarf wrapped around the neck, along the entire length of which there are transverse stripes of different colors,” explains Katherine Pollard, director of the study, director of the Gladstone Institute for Data Science and Biotechnology in San Francisco. in a different order, making some strips narrower and others wider and winding them again, it will be a completely different scarf. This is roughly what happened. jpg» media-type=»photo» data-crop-ratio=»0.933454876937101″ data-crop-width=»600″ data-crop-height=»560″ data-source-sid=»» class=»lazyload» lazy =»1″ />
In the zones of accelerated development, there are enhancers — transcription enhancers that can affect the activity of nearby genes. As a result of a DNA restructuring that occurred in human ancestors a million years ago, the genes responsible for brain development accidentally ended up next to HAR enhancers. And it was a turning point in the history of our species.