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False twins: individuals who are identical but not related

Throughout our lives, we often encounter individuals who remind us of someone we know, be it a friend, family member, or acquaintance. Have you ever wondered why this happens? Well, in this article, we delve into the fascinating world of 'unknown twins.' An intriguing study using facial recognition algorithms and DNA analysis discovered that facial resemblance between individuals is closely associated with our genetic differences.


 

Are there people who, without being twins, look alike?


Genetics, once again, provides the answer to this intriguing puzzle. A study, which focused on identifying physically similar individuals—32 pairs in total—offered a genetic perspective on these particular cases.


The identification of these pairs sharing physical resemblances was conducted through the photographic work of François Brunelle, a Canadian artist who, since 1999, has captured images of physically similar people without any familial ties in various parts of the world.

Figure 1: Unrelated look-alikes photographed by François Brunelle.
Figure 1: Unrelated look-alikes photographed by François Brunelle.

To verify the absence of relatedness among these pairs, the study employed Identity by Descent (IBD) analysis. Surprisingly, it was found that only one pair shared genetic variants in proportions similar to third-degree relatives. However, for the remaining pairs, despite the apparent resemblance (as depicted in Figure 1), the existence of any degree of relatedness was completely ruled out.


 

The genetics behind this phenomenon


In addition to studying the unknown twin set (LAL in Figure 2), the analysis included monozygotic or identical twins (MZ-twins in Figure 2) and individuals without physical resemblance or familial relationship (Non-LAL in Figure 2). This inclusion allowed for a comprehensive comparison among the three groups through DNA analysis, enabling the creation of a similarity score between them.

Figura 2. Similitud entre los gemelos monocigóticos o idénticos (MZ-twins), gemelos desconocidos (LAL) y personas sin parentesco y sin similitud física (Non-LAL).
Figura 2. Similitud entre los gemelos monocigóticos o idénticos (MZ-twins), gemelos desconocidos (LAL) y personas sin parentesco y sin similitud física (Non-LAL).

The results unveiled a statistically significant similarity score among the three groups. This confirms that, at a genetic level, there is indeed a resemblance among unknown twins, although it is much greater than observed in the "Non-LAL" individuals and lower than that observed in monozygotic or identical twins.


In Figure 2, the comparative analysis of similarity is depicted among monozygotic or identical twins (MZ-twins), unknown twins (LAL), and unrelated individuals without familial resemblance (Non-LAL).


Upon a more detailed analysis, it was observed that among all examined genetic variants, 113 of these genetic variations (SNPs) were associated with specific facial characteristics or physical traits.


The study we refer to demonstrates that unknown twins share genetic variants in their DNA. This doesn't denote relatedness, but rather, by chance, identical DNA sequences or regions are created in various individuals.


Due to the challenge of acquiring such data, the sample size is small, limiting the capacity for large-scale statistical analyses. Additionally, it's essential to note that the study focused solely on SNPs, preventing the analysis of other genetic components like structural variations.


Nevertheless, a collection of genetically unrelated but facially similar photos, combined with DNA analysis, has revealed that significant facial similarity is linked to shared genetic variants.




Written by Irene Rodríguez

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