Many people are interested in discovering the origins of their ancestors, and some of them opt to take ancestry tests to learn about their genealogy. However, if the genomes of humans vary on average by 0.1%, how is it possible that our ancestry can be determined through this test?
Follow along in the text to find out! We discuss how and why ancestry tests are conducted. Additionally, we talk about the different types, limitations, and how they relate to other genetic tests.
How is the ancestry test conducted?
In general, ancestry tests use samples collected through a buccal swab, which are then processed through molecular biology techniques. Genetic ancestry tests are conducted through molecular methods that allow for similarities to be found between the genome of the individual being tested and contemporary individuals belonging to certain geographic regions. The information obtained is then compared with reference genomes, allowing for the estimation of a person’s ancestry mixture, as well as the verification of relationships between individuals in a database.
Usually, microarray assays (SNP-Array, in most cases) are used so that thousands of genetic variants present in a DNA sample can be interrogated. The probes used in the analyses can be related to:
Autosomal DNA, used for inference of ancestry composition and genealogical trees;
Mitochondrial DNA (mtDNA) and Y-DNA, used in the determination of haplogroups (which can be geographically oriented).
Although less common, it is also possible to conduct ancestry testing through Next-Generation Sequencing (NGS). this technique allows for genomic analysis with greater precision, indicating any and all variations in the DNA sequence.
For example, Predicta Infinity, a genetic mapping exam offered by Einstein Genomics, informs about the risk evaluation for disease development, more effective medications for treatments, and also informs about ancestry, revealing your genetic origin.
What determines ancestry testing?
The calculation that indicates the genetic similarity between a DNA test and reference DNAs for certain geographic regions is possible because some specific genetic variants are present in individuals from a region and are used to represent the population of those locations.
This genetic representativeness occurs both because certain variants can be highly frequent in certain populations or because they can be associated with particularities of some populations of known geographic origin.
In other words, these genetic tests rely on the idea that the frequency of some genetic variants tends to be different between Latin American, Asian, and European individuals, for example. It is from this notion that a particular genome is compared with others, and its level of similarity is inferred in terms of ancestral composition. However, this raises a pertinent question: are ancestry determination calculations accurate?
Types of Ancestry Tests
Ancestry tests available on the market are offered in different ways. Some only seek to infer a person’s geographic ancestry, using genomes that are more or less representative of a particular location as a reference.
Other tests also offer the possibility of structuring a family’s genealogy. In other words, tests allow a person to identify others as belonging to their family. In this case, companies maintain databases to relate related individuals.
Some ancestry tests are also accompanied by the analysis of genetically recognized pathogenic variants, as we will see later. In this case, the inferred information is related to an increase (or decrease) in genetic predisposition to some diseases.
Is Ancestry Testing Reliable?
To answer this question, it is important to note that an ancestry test is performed by comparing segments of a person’s genome with genomic segments (available in a database) of individuals currently living in different regions of the world.
We do not have access to the genome of truly ancestral populations, so ancestry is inferred from existing descendants in different geographic regions.
In addition, obtaining representative isolates of a particular population is a difficult task. For example, the genome of contemporary individuals from the northern African continent may not adequately represent the genomic identity of the people who lived in this same region centuries ago when they were brought to the Americas.
Similarly, several populations have many fewer people today than at other times in history. In the case of indigenous populations, for example, the reduced genetic diversity of these populations today represents a limitation of the tests. This is because, even when available as a reference, these genomes may not perfectly represent the genetic diversity of ancestral indigenous peoples.
Thus, the accuracy of geographic ancestry inference depends on the available genetic databases, as these are the data to be used as reference representation for certain population groups.
Practically speaking, laboratories that perform these tests must be careful to avoid biases, such as those arising from the fact that many genetic databases are composed of genomes of European origin.
Certain genetic variants are distributed geographically in such a way as to represent populations from different parts of the planet. It is important to note that species evolution is not limited to state territoriality, and therefore ancestry is related to regions and not countries.
The results and interpretation of ancestry tests depend on how and which genetic databases are used by the laboratory that performs these tests. The details and specifications of how these assays are conducted are not usually disclosed by these laboratories. This is due to commercial and often ethical concerns.
Consequently, when we wish to perform an ancestry test, we should turn to excellent laboratories whose service quality is recognized and referenced by society. This way, it is possible to minimize the limitations raised so far, especially in cases where the ancestry test is performed with health issues in mind.
Detectable genetic diseases
We know that certain genetic variants are pathogenic, meaning they can influence the course of the development of one or more diseases. With this in mind, many people seek ancestry tests wanting to know if they have this type of variant in their genome.
Many of the commercially available ancestry tests additionally offer this service. The calculation of the Polygenic Risk Score is an important tool in a geneticist’s office and allows individuals to take care of their health more precisely.
However, when these scores are analyzed without the assistance of a qualified doctor who understands the nuances of an exam, this information ends up having an uncertain scientific and clinical meaning, similar to the inference of ancestry.
If you want to investigate your own genetic material for health purposes, Varsomics recommends that genetic tests in general be performed with a geneticist doctor who is capable of offering genetic counseling.
Ancestry tests aim to infer an individual’s geographic ancestry, as well as establish relationships of kinship between people. These tests are usually performed from a nasal swab sample. This sample is subsequently processed by molecular biology techniques, such as SNP-Array.
In this technique, hundreds of thousands of points in the sampled genome are investigated and compared with reference genomes for certain locations on the planet. Ancestry tests have intrinsic limitations, largely related to the genetic diversity of the databases, as well as the difficulty of obtaining truly representative references of the ancestral populations of a given region.