Since the discovery of such a phenomenon as horizontal gene transfer, namely not from parents to offspring, the entire living world on our planet has been represented as a single information system. And in this system it becomes possible to borrow a successful evolutionary invention of one species by another. What is vertical and horizontal gene transfer, what are the mechanisms of this process and examples in the organic world - all this is the article.
Neighbour genes
Everyone knows that we get our genes from our parents. And they are from their parents. This is the vertical transfer. And if suddenly a mutation occurs that turns out to be useful for survival or adaptation, and gains a foothold in the genome of the population, then the species will gain advantages in the struggle for existence.
At the same time, a person has his own genes,aphids have their own, and sharks have their own. It is almost impossible for them to get between species. But sometimes it happens - this is horizontal gene transfer.
This is what modern genetic engineering does. Genetically modified organisms are the result of such gene transfer (for example, the luminous tardigrade in the photo above). But in nature, this phenomenon has existed for a long time.
The heart of the matter
Vertical gene transfer is the phenomenon of the transfer of hereditary material from parental forms to daughter organisms.
Horizontal gene transfer is a natural situation of transferring genes from one adult organism to another. At the same time, two organisms objectively exist, and sometimes they belong to different biological species.
An example of horizontal gene transfer in bacteria is the transfer of resistance genes from one bacterial strain to another.
Necessary conditions
To understand this phenomenon, it is necessary to know the conditions under which such a transfer is possible in principle, namely:
- It is necessary to have an intermediary for the "transport" of genes from one cell to another, from one organism to another.
- There must be a molecular mechanism that would allow foreign genes to be inserted into the host's gene set.
These conditions may well be fulfilled by retroviruses and other transposons (DNA elements). And it is precisely such methods of horizontal gene transfer that genetic engineering has adopted today.
AlthoughToday, the mechanisms of such gene transfer are only being studied; in addition to viruses, such transfer can also occur with the help of free sections of deoxyribonucleic acids (transposoons), which enter the body through a simple introduction or with parasitic organisms. The latter can change not only the host's genetic apparatus, but also its ecological place in the biocenosis system.
Background
It was the transfer of antibiotic resistance genes between different bacterial strains that was first described in Japan in 1959.
Already by the mid-1990s, molecular biologists proved that horizontal gene transfer in prokaryotes and eukaryotes was involved in the evolutionary development of life on our planet.
In 2010, a study by Professor Cedric Feschott was published, which presented an analysis of the genome of the opossum and saimiri monkeys. They were bitten by one kind of bug. In the genomes of mammals, a transpozoon has been found that has 98% identity with insects. For your information, these bugs bite not only monkeys and opossums.
From now on, the hypothesis of horizontal gene transfer between different domains of organisms has become a new paradigm of biology.
Colorful bugs
And if the horizontal gene transfer in bacteria for the last 30 years has not raised doubts among biologists, then its possibility in multicellular organisms has raised many questions. It was then that the attention of biologists was attracted by the common aphid, in whichthere are individuals with green and red color of the body.
An analysis of the pigments that give color to red individuals revealed the presence of carotenoids - plant pigments. Where did aphids get genes that are unique to plant organisms? Today, sequencing the insect genome is a fairly simple matter for researchers. This is how it was discovered that the genes of aphids responsible for the synthesis of red pigment are completely identical to those of some fungi that parasitize in the body of aphids without causing any visible harm.
Most likely, at the dawn of aphid evolution (about 80 million years ago) there was a failure in the genetic machine and the fungal genes were built into the insect genome.
Evolution and biodiversity
All phylogenetic systematics of the organic world is based on Darwin's concept of divergence. Its essence is as follows: as soon as reproductive isolation occurs between populations of a species, we can talk about the process of speciation. And already two species continue to evolve based on natural selection and random mutations.
The discovery of horizontal gene transfer between species and larger taxa only proved that in such a short time (4 billion years) by cosmic standards, living matter on our planet could go from unicellular forms to highly organized multicellular ones.
Thus, the entire biota of the planet becomes a single laboratory for the creation of new hereditary traits, and it is the horizontal movement of genescould and continues to significantly accelerate the evolutionary process.
Let's borrow some genes
In 2015, geneticist Alistair Crisp from Cambridge (UK) studied the genomes of 12 species of fruit flies Drosophila, 4 species of roundworms and 10 species of primates (one of which is a human). The scientist was looking for "alien" sections of DNA.
Research results have confirmed the presence of 145 regions in the genomes that are the result of horizontal gene transfer in eukaryotes.
Some of these genes are involved in the metabolism of proteins and lipids, the other - in immune responses. Most importantly, it was possible to identify probable donors of these genes. They turned out to be protists (the simplest eukaryotes), bacteria (prokaryotes) and fungi.
What about us
It is already reliably known that through horizontal gene transfer in humans, the genes responsible for blood types AB0 appeared.
Most of the evidence for such gene transfer in primates is of very ancient origin, dating back to a common ancestor with other chordates.
According to recent studies, the formation of the placenta in humans is also responsible for the gene of the virus, which was captured somewhere at the dawn of the formation of placental animals.
The results of sequencing of the human genome showed that it contains about 8% of pieces of viral genomes, which are called "sleeping genes".
The Age of Mutants
Here we come tothe topic of horror stories with which green activists scare. What if these "sleeping" genes turn on? Or is a tick biting a person and pulling some kind of horror into his genome? Or do we eat genetically modified soybeans and become mutants? But after all, for 4 billion years, the biodiversity on the planet has only increased, and you and I are still a little like whales, like aphids are like mushrooms. Why is that?
Firstly, the mechanism of horizontal transfer exists in nature as long as life itself exists. And on the example of aphids, it is perfectly clear that such gene transfer was aimed precisely at increasing the adaptability of organisms to environmental conditions (red ones are less visible on certain parts of plants). And genetic engineers in this sense did not come up with anything new. Tomatoes with arctic fish genes have increased cold tolerance, which allows them to be grown in northern regions.
Secondly, despite the possibility of genetic transfer, we do not yet observe the unification (uniformity) of the genome of all living organisms on the planet. The stability of the biological system, which is the cell and the organism, is high enough to limit inefficient gene transfer. But at the same time, it is precisely this transfer that is the instrument of biological evolution, which leads to biodiversity. So it won't be long before bears look like kites, and dogs look like chameleons.
