Understanding Zero Matches in DNA Tests: 0% Unlikely But Not Impossible

Have you ever wondered if a DNA test could say zero match in terms of relatives or ethnicity estimates? The answer lies in the intricacies of genetic testing and the probabilities involved. Let's break it down for you.

Probability of Matching DNA with Relatives

When conducting DNA tests, it's important to understand the probabilities involved in matching results. Even with closely related individuals, such as second cousins, there is always a chance of no DNA match. This is because the genetic material can get distributed in different ways, resulting in different segments of DNA being passed to each person.

For example, up to second cousins, who share a great-grandparent, there is a 100% chance of some DNA sharing. However, the amount of shared DNA typically ranges between 1 and 5%. This means that, statistically, the chance of a second cousin sharing any DNA at all is extremely high, but the amount shared is usually minimal.

Zero DNA Matches in List of Matches

While it's possible to have a zero match in terms of ethnicity estimates, the list of DNA matches you receive from a company like Ancestry DNA is unlikely to show zero DNA matches. This is because these companies typically do not show matches that are below a certain threshold, usually 20 centiMorgans (cM).

This means that if you receive a DNA match list from a service, you will always see at least some amount of shared autosomal DNA, no matter how small the percentage may be.

Calibration and Measurement in DNA Tests

When it comes to genetic tests, there are many ways to calibrate and measure the results. However, if a method is chosen that makes it mathematically impossible to get a negative number, then getting a value of 0.00000 is mathematically impossible as well and would be extremely rare.

The key feature that makes a result of zero unlikely is that the test relies on many separate measurements. Each measurement contributes to the final result, making it statistically improbable to get a net result of zero. This is because it's highly unlikely to get a large number of measurements that would perfectly cancel out to zero.

However, it's important to note that reporting rules can sometimes override this. For instance, in some commercial tests for contaminants like lead or mercury in water, values lower than a certain threshold might be reported as zero. This is a potential loophole that should be considered.

Conclusion

In conclusion, while a DNA test can theoretically state a 0% match, the probability of this occurring is extremely low. The likelihood of a zero match in terms of ethnicity estimates is also very slim due to the nature of genetic tests and their threshold settings. Understanding these nuances can help you better interpret your DNA test results.