Since the discovery of such a phenomenon as horizontal gene transfer, namely, not from parents to descendants, the entire living world on our planet seems to be a single information system. And in this system, it becomes possible to borrow a successful evolutionary invention of one species by another. What is the vertical and horizontal gene transfer, what are the mechanisms of this process and examples in the organic world - this is all about this article.
Neighbor's genes
Everyone knows that we get our genes from our parents. And they are from their parents. This is vertical transfer. And if suddenly a mutation occurs that is useful for survival or adaptation, and is fixed in the genome of the population, the species will gain advantages in the struggle for existence.
Moreover, humans have their own genes, aphids have their own, and sharks have their own. There is practically no way to get them between the species. But sometimes this 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 tardigrades in the photo above). But in nature, this phenomenon has existed for a long time.
Essence of the question
Vertical gene transfer is the phenomenon of the transfer of hereditary material from parental forms to daughter organisms.
Horizontal gene transfer is a naturally occurring situation of gene transfer from one adult organism to another. At the same time, two organisms objectively exist, and sometimes belong to different biological species.
An example of horizontal gene transfer in bacteria is the transfer of resistance (resistance) genes from one strain of bacteria to another.
The 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.
- A molecular mechanism is needed that allows the incorporation of foreign genes into the host gene set.
The aforementioned conditions may well be fulfilled by retroviruses and other transzoozones (DNA elements). And it is precisely these methods of horizontal gene transfer that have been adopted today by genetic engineering.
Although today the mechanisms of such gene transfer are only being studied, except for viruses, such transfer can also occur with the help of free sites of deoxyribonucleic acids (transzoons), which enter the body through a simple drift or with parasitic organisms. The latter can change not only the genetic apparatus of the host, but also its ecological place in the biocenosis system.
Background
It was the transfer of antibiotic resistance genes between different strains of bacteria that was first described in Japan in 1959.
By the mid-90s of the last century, molecular biologists had 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 possum and the Saymiri monkeys. They were bitten by one type of bug. A transposon was found in the mammalian genomes, whose identity with the insect is 98%. For information, these bugs bite not only monkeys and possums.
Since that moment, the hypothesis of horizontal gene transfer between different domains of organisms has become a new paradigm in biology.
Multi-colored insects
And if the horizontal gene transfer in bacteria over the past 30 years has not raised doubts among biologists, then its possibility in multicellular has raised many questions. It was then that the attention of biologists was attracted by ordinary aphids, in which individuals with green and red bodies of the calf are found.
An analysis of the pigments that color the red individuals revealed the presence of carotenoids - plant pigments. Where did the aphids come from genes that are unique to plant organisms? Today, sequencing the bug genome is a fairly simple matter for researchers. This is how it was discovered that the aphid genes responsible for the synthesis of red pigment are completely identical to that of some fungi that parasitize the aphid's body without causing any visible harm.
Most likely, at the dawn of the evolution of aphids (about 80 million years ago), there was a malfunction in the genetic machine and the fungal genes were embedded in the bug genome.
Evolution and Biodiversity
The entire phylogenetic systematics of the organic world is based on the Darwin concept of divergence. Its essence is as follows: as soon as reproductive isolation arises 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 has only proved that in such a short space time (4 billion years) living matter on our planet could go from unicellular to highly organized multicellular organisms.
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 genes that could and continues to significantly accelerate the evolutionary process.
Borrow some genes
In 2015, geneticist Alistair Crisp from Cambridge (UK) conducted a study of 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.
The research results confirmed the presence of 145 regions in the genomes, which were 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 (protozoa eukaryotes), bacteria (prokaryotes) and fungi.
And what about us
It is already reliably known that through horizontal gene transfer in humans, genes responsible for blood groups AB0 appeared.
Most of the facts of this gene transfer in primates has a very ancient origin and dates back to the existence of a common ancestor with other chord animals.
According to recent studies, the formation of the placenta in humans is also responsible for the virus gene, which was captured somewhere at the dawn of the formation of placental animals.
Sequencing of the human genome has shown that it contains about 8% of pieces of viral genomes called “sleeping genes”.
Era of mutants
So we come to the topic of horror stories that scare green activists. What if these “sleeping” genes turn on? Or does a tick bite a person and drag some horror to it in the genome? Or do we eat genetically modified soybeans and become mutants? But after 4 billion years, biodiversity on the planet has only increased, and you and I are still a little like whales, as well as aphids - like mushrooms. Why is that?
First, the mechanism of horizontal transport exists in nature as long as life itself exists. And with the example of aphids, it can be clearly seen that such gene transfer was aimed specifically at increasing the adaptability of organisms to environmental conditions (red ones are worse seen in certain parts of plants). And genetic engineers in this sense did not come up with anything new. Tomatoes with genes of Arctic fish have increased cold resistance, which allows them to grow in the 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 body, is quite high and limits the ineffective gene transfer. But at the same time, just such a transfer is a tool of biological evolution, which leads to biodiversity. So soon bears will become like kites, and dogs - like chameleons.