The sound of genetics often has a fatalistic ring to it. But is that true? Can something really be “in your genes”? If a person has a genetic predisposition to a trait, are they predestined to have it?
Genes determine only a part of your fate
People tend to think that the genes you inherit from your parents explain and define who you are, but this is not the case, especially for polygenic traits. And a lot of traits are polygenic.
Based on your DNA, researchers can estimate your chance of developing a trait, commonly called “genetic predisposition” or “genetic susceptibility”. However, for polygenic traits, the relationship between a genetic predisposition and the actual outcome can be very fuzzy. This is because other non-genetic factors will play a role in this process. Birth complications, eating habits, being read to, going to school, playing sports, different kinds of illnesses: the list goes on.
So, having a genetic predisposition to a polygenic trait does not guarantee that you will develop it, but it means that you are more likely to. Nowadays, there are personal genomics companies (like 23andMe and Ancestry DNA) that use a sample of your DNA to work out the probability of developing a trait. In case you have done one of these tests, keep in mind that predisposition to a polygenic trait is not set in stone.
On top of that, scientists make an even stronger case for how genes don’t determine your fate. There are two main reasons for that: environment matters, and the population used in the study matters.
Environment matters
Very often, the development of a trait is a combination of genetics and environment. Let’s take reading as an example. Researchers have shown that genetics plays a role in how well people can read: overall, according to studies that investigate twins, up to 50 percent of people’s reading ability may be related to genetic factors. In other words: you can have a talent for reading.
But there’s more: besides learning to read at school, you practice your reading skills with every book you read. So apart from genetics, other factors contribute to how well people can read, including how many books the parents have at home, how often they read to their child, and how often you practice.
This means that even though someone may have a low genetic predisposition for reading, they may read a lot because their parents have many books at home and develop their reading skills. Recently, researchers have found that reading skills predict how much you enjoy reading and not the other way around. On the other hand, people with high genetic predisposition for reading ability still may not read well if they don’t practice.
The population used in the study matters
When geneticists observe a relationship between DNA and a trait of interest, this can depend on the participants who took part in the study (in other words, the population). When you receive an estimate of your genetic predisposition for a trait, someone has had to analyse your DNA and compute this genetic predisposition based on some kind of DNA reference. And that reference has come from a published study. So, of course, the results will be influenced by which participants (what population) took part in that reference study. In addition, when you take a DNA test your genetic predisposition is compared to that of other users who also took the test with the same company.
The characteristics of the reference population matter. The problem is that researchers usually don’t know how the findings from one population apply to populations with other characteristics. And something to highlight here is that most of the published genetic studies are based on individuals with European ancestry. For example, findings from a study on reading ability in a country where literacy is very common may not be so good at predicting how well people read in a different country where few people have access to books. Regardless of genetic factors, without access to teaching and books (or other written material) it is unlikely that a person will develop good reading abilities.
In short, how applicable is the genetic predisposition for each person? That will depend on how similar the background of that person is to the population used in the reference study.
Writer: Lucia de Hoyos
Editors: Jitse Amelink, Else Eising
Translation Dutch: Izabela Jordanoska
Translation German: Anna Serke
Recommended readings
- Rajagopal, Veera M. “A deep dive into the dark regions of the human genome.” GWAS stories, 19 Jan 2024, gwasstories.com/p/a-deep-dive-into-the-dark-regions. Accessed 27 May 27 2024.
- Dellwo, Adrienne. “Genetic predisposition and what it means”. Very Well Health, 6 May 2024, verywellhealth.com/genetic-predisposition-5087879. Accessed 27 May 27 2024.
- Harden, K.P. Genetic determinism, essentialism and reductionism: semantic clarity for contested science. Nat Rev Genet 24, 197–204 (2023). https://doi.org/10.1038/s41576-022-00537-x
