How can we pass on our DNA, other than to our children? Is there any other way to pass on genetic material other than through reproduction? The answer may surprise you as we explore horizontal gene transfer.
Vertical Gene Transfer
You know that the genes that make you who you are came from Ma and Pa, right? That is a clear-cut case of something known as vertical gene transfer, meaning genes are transmitted from parent to offspring during reproduction. But there is another funky way that genes can be transferred between organisms, and not just between parents and offspring. This kind of gene transfer can even occur between members of different domains: the eukaryota, bacteria and archaea. It’s called horizontal gene transfer.
Let’s go over it.
Horizontal Gene Transfer
Horizontal gene transfer, also known as lateral gene transfer, is the transmission of genetic material from one genome to another genome in a way other than reproduction. How can this be so? Well, there’s actually more than one way, and I’m going to give you a concrete example.
Let’s picture a small bacterial cell swimming about. All of a sudden, a bigger eukaryotic cell comes across it, and like an octopus, snatches it up. The bacterial cell then is trapped within the eukaryotic cell, where it is degraded by digestive enzymes, much like food in the stomach. In some instances, part of the bacterial genome is for some reason not degraded, and this bacterial gene can insert itself into a chromosome of a eukaryotic cell. Additionally, at least when it comes to bacteria, there are three main types of mechanisms by which horizontal gene transfer occurs that I want you to be aware of.
They are called transformation, conjugation and transduction. Transformation occurs when bacterial cells are moving about and come across short fragments of naked DNA in their environments, fragments they take up. In conjugation, two cells form a temporary bridge, or union upon which genetic material can be transferred from one cell to another.
In transduction, DNA is transmitted from cell to cell via a kind of virus called a bacteriophage. Basically, the DNA is injected into a cell by this virus, much like a syringe is used to inject something into your body.
Why is horizontal gene transfer important and how has it shaped evolution? We know that horizontal gene transfer has allowed bacteria to swap material that allows for antibiotic resistance.
That means they use horizontal gene transfer to evolve into slightly different bacteria, ones that can now survive our drug assault. Basically, bacteria used horizontal gene transfer to beef up their defense against our own defenses. This allows them to survive, reproduce, and beat back our weapons. But again, I mentioned that horizontal gene transfer can happen between members of different species, and even domains, not just members of the same species. Thus, its role in evolution goes far beyond just today’s ever-evolving antibiotic resistance. As an example of this, researchers know that many genes found in yeast, which are eukaryotes, have many more similarities to genes found in bacteria than genes found in archaea.
This hints at the possibility that eukaryotes may have a more recent common ancestor with bacteria than with archaea. How could this be the case? It could be that eukaryotes actually originated when two prokaryotes fused together, at least one of which was a bacterium. As another example, it’s suspected that genetic exchanges between a human cell, which is a eukaryotic cell and that of a bacterium, neisseria gonorrhoeae have occurred that have allowed the bacterium to survive in humans, giving us the pleasure of being susceptible to the sexually transmitted infection gonorrhea.
Horizontal gene transfer, also known as lateral gene transfer, is the transmission of genetic material from one genome to another genome in a way other than reproduction.
All this is saying is that one living cell transfers part of its genome to another cell, or captures a piece of genetic material from the environment. When it comes to bacterial cells, this happens in three ways: transformation, the uptake of DNA from the environment; conjugation, the passage of genetic material from one cell to another via a temporary union; and transduction, the transmission of genetic material from one cell to another via a virus. Horizontal gene transfer may have helped to form the domain eukaryota, has caused antibiotic resistance to occur, and has allowed organisms to infect our bodies.