You will be surprised to know that we are carrying non-human genes in our genome. Our genome is not completely human genome. I mean to say, we, human beings have some of the non-human genes (foreign genes) initially derived from some other organism during the course of evolution.
According to a recent study published in Genome Biology, human beings (every one of us) harbor about 145 foreign genes that were incorporated into our genetic material during the course of evolution. The source of foreign genes includes bacteria, viruses, and some other single-celled organisms.
Alastair Crisp, a biologist from the University of Cambridge said that the “tree of life” is not simply the stereotypic tree that has perfectly branching lineages. But in reality, it is more like one of the Amazonian strangler figs where the roots are more tangled with each other in a cross back way.
Horizontal gene transfer is the movement of the genetic information from one organism to another organism (not the parent to offspring inheritance). And we know that it is a common idea of many bacteria and simple eukaryotes to share an antibiotic-resistance set of genes to adapt themselves according to the environment. However, the possibility of horizontal gene transfer from these microorganisms to higher organisms such as primates has always been a disputed topic.
As in the case of bacteria, it has been proposed that the animal cells might have adopted the foreign genes that were introduced into the host cell as small fragments of genetic materials. However, it is quite tricky to prove that we have a bit of DNA in our genome that was originally derived from another organism.
To understand furthermore, Crisp and his colleagues performed a genome sequence analysis of 40 different animal species including fruit flies, roundworms, zebrafish, and some higher animals such as gorillas and human beings. They searched existing databases for close matches among the organisms of study and also among the other animals, non-animals (e.g. plants, fungi bacteria, and viruses).
While analyzing the genome sequence, they looked for a gene in an animal genome that matches more closely to a non-animal gene than any other gene from an animal genome. For this analysis, they used computational methods to be sure whether the initial database search had some missing things or not.
In human beings, researchers found 145 genes that came from simpler organisms, and 17 out of 145 genes had been reported to be a result of the horizontal gene transfers. This shows that the horizontal gene transfer is not limited only to the microorganisms but it has also played an important role in the evolutionary journey of many animals.
These genes are involved mainly in metabolism, and many other basic biochemical processes. However, it is still not clear about the mechanisms of how these genes were transferred and its exact timeline when these genes jumped into the human genome.
This paper makes it clear that there is an existing evolutionary history of horizontal gene transfer between organisms. However, most of the researchers agree that it is not completely indisputable evidence.
Jonathan Eisen, a microbiologist from the University of California, Davis, said that there is a little convincing evidence for horizontal gene transfer between bacteria and animals. However, there are some other explanations for the identified genes that are present only in some of the branches of the evolutionary trees.
These are the genes that existed in a far-off ancestor and could have simply lost in many other relatives during the course of evolution. He said it’s up to the researchers to exclude other and more plausible alternatives.
Reference: Genome Biology
Article doi: 10.1186/s13059-015-0607-3