Have you ever crossed paths with someone on the street who looked suspiciously like you? They are called Doppelgängers, and although folklore says it is a bad omen, science has a much more fascinating explanation: the maths of genetics.
We share more than 99.9% of our DNA with any other human being. It is in that small 0.1% where the magic of our differences... and our similarities occurs. However, when we analyse that code in a genetic test, a very common confusion often arises among our users:
"The test says I have a high probability of having light eyes, but my eyes are brown! Is the result wrong?"
The short answer is: No, the result is not wrong. The long answer forces us to differentiate between two key concepts: what your genes say (genotype) and what you see in the mirror (phenotype).
Probability vs. Reality: We are not binary code
When at tellmeGen we analyse your traits, we are not "looking" at a photo of your face. We are reading the instruction manual with which you were built.
Many physical traits do not depend on a single gene (monogenic), but are polygenic. That is, they are the result of a complex vote among thousands of genetic variants. Furthermore, the environment and other biological factors can "switch off" or "switch on" certain instructions.
That is why we speak of genetic predisposition. Your DNA might say "I have every chance of having blue eyes", but if an external factor or an unknown genetic variant intervenes, your iris may appear darker.
1. The Gaze
What plays a part in your eye colour? Although we analyse the predisposition to eye lightness, the final proportion of pigments can be affected by multiple metabolic pathways.
And it is not just the colour. Details like the presence of pigmentation rings in the iris (those darker rings around the pupil) or the eye structure depend on very subtle genetic nuances. Your genetics mark the trend, but biology decides the final tone.
2. Hair and skin
Something similar happens with skin and hair. Your genetics dictate your basal levels, such as your cutaneous melanin levels, which determine how dark your base skin is. But we all know that the sun can change that drastically.
The same happens with hair. We can predict with great accuracy your probability of being a redhead (thanks to the study of the MC1R gene) or your predisposition regarding blonde or dark hair tonality. However, hair shape (straight, wavy or curly) can be altered by hormones, age or even the humidity of the climate where you live.
3. The passage of time and "imperfections"
Sometimes, what makes us look like another person are not the "pretty" traits, but the shared "problems". Genetics influences enormously how our skin withstands the passage of time.
Facial ageing is not the same for everyone; for example, some genetic variants help protect collagen better than others. Similarly, the predisposition to suffer from acne vulgaris is highly heritable, although stress, diet and hormonal changes are the final triggers.
4. The small details
Finally, there are those morphological curiosities that make you unique (or identical to your double). Have you noticed your teeth? Tooth morphology, such as having wider or crowded front teeth, has a heavy genetic load.
Or something as subtle as your ears. Whether you have attached or detached earlobes is one of those genetic signatures that, although they seem simple, help define the geometry of your face.
That the result of your genetic test does not coincide 100% with what you see in the mirror is not an error; it is a biology lesson. The test tells you what your DNA planned to build; your body is what was finally built.
Knowing your predisposition to all the above is important not only out of curiosity, but to understand how your body works. If your genetics say you have light skin, but you are very tanned, you know your skin is working overtime to protect itself.
So, the next time you see your results, remember: you are reading the mathematical probabilities that made you you.
If your curiosity has been piqued and you want to discover what the "blueprints" of your body really say —from why you have that eye colour to how the passage of time will affect you— do not remain in doubt. Get your tellmeGen DNA test and start exploring the science that makes you unique.
