The MyHeritage DNA test is a form of autosomal testing, which analyzes the 22 pairs of non-sex chromosomes inherited from both parents. The test provides two main sets of data: an Ethnicity Estimate, a percentage-based breakdown of ancestral origins, and a list of DNA Matches, which identifies potential relatives. Determining the accuracy of the results depends entirely on which aspect of the report is being considered, as accuracy is measured differently for each of these two distinct components.
How MyHeritage Calculates Ethnicity Estimates
The Ethnicity Estimate is a statistical prediction of where one’s ancestors lived thousands of years ago, based on an analysis of sampled genetic markers. MyHeritage, like other companies, examines hundreds of thousands of specific locations on the DNA strand called Single Nucleotide Polymorphisms (SNPs). These SNPs are the tiny variations in the genetic code that differ between individuals and populations.
The company compares the DNA profile of the user to a proprietary reference panel, a curated collection of DNA samples from individuals whose families have lived in a specific region for many generations. These reference populations act as genetic signposts for particular geographic and ethnic groups. If a segment of a user’s DNA closely matches the patterns of the samples in the reference population, that segment is assigned that origin.
The genome is computationally divided into smaller sections, and each section is statistically assigned to the most probable reference population. This approach means the resulting percentages are estimates, reflecting probabilities rather than definitive, exact ancestral locations. The results are a snapshot of the genetic similarities between the user and the current reference panel.
The statistical modeling often makes it challenging to distinguish between closely related populations or those with a history of shared migration patterns. For instance, distinguishing between various populations within the British Isles can be difficult due to extensive historical movement. Because the process relies on statistical probability and comparison to a finite data set, the ethnicity breakdown is seen as a genetic interpretation of ancestry, which is why the term “estimate” is used.
The Reliability of DNA Match Identification
The accuracy of genealogical matching is considered much higher than ethnicity estimation because it relies on the biological reality of shared DNA inheritance. MyHeritage identifies potential relatives by comparing the user’s DNA against every other user in its database to find shared segments. The length of these shared segments is quantified using a unit of measurement called the centiMorgan (cM).
A centiMorgan represents the probability that a segment of DNA will be separated by recombination over generations, making it a proxy for genetic distance. The total amount of shared cM correlates directly with the closeness of the relationship. For example, a parent and child will share approximately 3,400 cM, while a first cousin will typically share around 850 cM.
MyHeritage uses the shared cM value to predict the possible relationship, often providing a probability range for different connection types. The company has a tool that can further fine-tune these predictions by incorporating the age of the two individuals, which helps narrow down the generational gap. For closer relatives, such as a parent or full sibling, the cM shared is so large that the prediction is highly reliable.
For more distant relationships, accuracy is best assessed by examining the characteristics of the shared DNA segments. Segments larger than 15 cM are considered highly reliable indicators of a true common ancestor. Conversely, very small segments, particularly those under 10 cM, have a much higher chance of being identical by chance, a phenomenon known as Identical by State (IBS), which does not indicate recent shared ancestry. Verifying a match’s validity can be accomplished using triangulation, which involves confirming that the user and two different matches all share the exact same segment of DNA, pointing to a single common ancestor.
Factors Affecting Result Consistency and Limitations
Several external and inherent factors contribute to the consistency and limitations of MyHeritage DNA results. One significant factor is the overall size of the DNA database, which directly impacts the quantity of relatives identified and the resolution of the ethnicity estimate. A larger database increases the chance of finding matches and provides a better pool of data for refining population groups.
The results users see can change over time because MyHeritage frequently updates its reference panel and computational algorithms. As more people from diverse geographical regions take the test, the reference panel becomes more detailed, allowing the company to distinguish between populations with greater granularity. These updates often result in minor shifts in the user’s ethnicity percentages.
Variability in ethnicity results between different testing companies is common and stems from the use of proprietary methodology. Each company maintains its own unique reference panel and employs a different algorithm to process the raw genetic data. Furthermore, different companies may analyze slightly different sets of SNPs, which can also contribute to variations in the final ethnicity breakdown.
A fundamental limitation of autosomal DNA testing is the random nature of genetic inheritance. While a user may know a recent ancestor had a small percentage of a specific ethnicity, the user may not have inherited any of the corresponding DNA segments. This is because only 50% of each parent’s DNA is passed down, and this random process can effectively dilute or eliminate small ancestral contributions over a few generations.