With DNA Matching, you can get the genetic results for the two people who took an autosomal DNA test, and the genealogical information available on each of them.
A DNA Match between two people can indicate that they are actual relatives, or that they share the same ethnic or regional background. It is therefore important to consider any genealogical information available (i.e. when the matching individual has a family tree).
For every DNA Match, you will see three different genetic parameters which allow you to compare matches pointing out similar possible relationship:
Shared DNA shows you the percentage of DNA that overlaps between you and the other person. In brackets, you can see the length of total shared DNA in centiMorgans (cM) — like meters or miles, this is the unit that describes the length of DNA segments. Seeing how much shared DNA you and your match have in common is the easiest way to get a sense of how closely related you probably are. For example, siblings share an average of 50% of their DNA, and the percentage goes down as the relationship gets more distant.
Shared segments: A segment is a piece of your DNA sequence. You and your DNA Match share a certain number of these segments in common, and some of them are longer than others. Your total shared DNA with another person is made up of lots of small segments, a few big segments, or some combination of both.
Largest segment: Among the different-sized shared segments, the length of the largest segment you and the other person have in common can help you identify the likelihood that you are actually related. The longer the largest segment is, the higher the chances that you’re related (e.g. a very long shared segment may reveal a possible relationship of 1st–2nd cousin). Looking at the length of the largest segment is also the easiest way to see the difference between a number of matches that all show the same possible relationship.
The possible relationship is calculated based on the genetic results presented to you. Although several matches might appear to describe the same relationship (e.g. 4th–5th cousin), they may in fact differ from one another based on the other parameters. It’s therefore recommended that you review all parameters for the most accurate understanding of each DNA Match. From there, you may review any available genealogical information, and contact the matching individual.