All humans share a huge part of our genome, 99.6%. That means that we are only different in that remaining 0.4%. We are so equal because the genome is what defines us as humans, but due to that 0.4% variability no two identical genomes exist. These divergences are responsible for our physical differences, which are the most obvious, but also for other traits, which I will comment on later.
Since we inherit the genome from our fathers and mothers, it will be more similar to theirs, but even so, it will have a small part different. Only in the case of twins who are identical, their genome is practically the same, but even they have some small differences. In fact, it is said that our genome is more important in identifying us individually than our fingerprint, which we all know is unique. We each also have our unique genome. For that reason, you will surely be familiar with paternity tests or the use of DNA to identify people related to crimes. This is possible because each person’s genome is different from that of the rest of humans.
Another interesting fact is that this 0.4% difference is not the same in all individuals. Yes, there are areas that we know are more variable and are more different between people, and that can be related to different characters (physical, hormone generation, immune system…) and there are also areas of the genome that are very variable between people of the same type. We still don’t know what they are for. But it is very important that they exist, since it is what allows humanity as a species to survive and be healthy. In fact, you will surely be familiar with the fact that when there are offspring among members of the same family, diseases often appear. These diseases have their origin in the fact that two very similar genomes have been mixed.
Regarding the different parts of the genome, we can say, very broadly, that they determine physical and psychological characteristics and also the risk of suffering from some diseases, such as hereditary cancer. These differences in the genome do not cause cancer per se, but they do put a person at greater risk of suffering from the disease throughout their life. By transmitting the genome to children, they may also have that increased risk. That is to say, the differences in our genome are not only related to the physical part, which is the most obvious, but they can also affect our health.
So that you understand this perfectly, I am going to give you a simple explanation of what the genome is. It is like the instruction manual of an organism. All living beings are made up of cells. These cells would not know how to function if they did not have an instruction book that tells them what to do and when to do it. That instruction manual is the genome, which is made of DNA. If we imagine our genome as a book, this DNA would be the language with which the instruction manual is written.
It is important that this manual be well written and well organized. If we had a user manual for a machine, for example, the first instruction would be to turn it on, the second to press a certain button, etc. The same thing happens with the genome, it is a manual that has organized the instructions that cells need to know what they have to do and when, and each instruction is what we call a gene. And depending on what cells they are, they receive some instructions or others. For example, liver cells do not do the same thing as eye cells, so the genome gives them the precise instructions that each of them needs.
The number of instructions that our genome encodes to regulate the functioning of cells is very large. That’s why our genome, this instruction manual, is huge. However, it is found within our cells, which are microscopic. Thus, this DNA must be very well compacted to concentrate that enormous amount of instructions in a space as small as a cell.
Laia Bonjoch She is a doctor in biomedicine, a researcher at the August Pi i Sunyer Biomedical Research Institute (IDIBAPS) in Barcelona.
Question sent via email by Esau Zamora Moreno.
Coordination and writing: Victoria Toro.
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