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The following article concerning genetic distance comes from the Family Tree DNA website.

Some Family Tree DNA customers will have Y DNA 12 Marker Exact matches with other surnames, and on a rare occasion, a 25 Marker Exact match with another surname. Most likely these people are not related in a genealogical time frame.

To understand how this situation occurs, we start by looking at the population before the origin of Surnames. Before the adoption of Surnames, there existed various Y DNA 12 Marker and 25 Marker results in the male population. The quantity of persons with any particular Y DNA result varied, based on their success of having male children, the survival of the male children, and how many of the male children procreated more male children. There was also migrations throughout the world. In addition, during this time, Markers continued to mutate, just as they do today.

Surnames began to be introduced and adopted at different rates in different countries, typically with the upper classes adopting surnames initially.

Different persons through out a region of the world population would have had the same 12 Marker result at the time of the introduction of surnames. This situation would have occurred due to some of the people being related and the others as a result of Convergence.

For more information on Convergence, see the Facts and Genes Vol. 1, Issue 5, the article titled "Haplotypes: Convergence".

As the adoption of surnames occurred, different persons with the same 12 Marker result most likely adopted different surnames. For example, perhaps there was a person in London who adopted the surname Barker and another person existed in Scotland with the same 12 Marker result, and they adopted the surname MacGregor. Assuming that there were no mutations, the descendants today would have a 12 Marker exact match, but they are not related in a genealogical time frame.

The key element in evaluating 12/12 Matches and 25/25 matches is the time frame. We are all related at one point in time. For our family history research, we are most likely only interested in a genealogical time frame. The genealogical time frame most likely does not start before the adoption of surnames, so the first requirement to determine relatedness is the surname.

The Marker mutation rate does not care about surnames, or whether the person even had a surname. Markers mutated before surnames and after the adoption of surnames. By utilizing the criteria of surnames, you are establishing the time frame for evaluating relatedness.

If two people match 12/12 or 25/25 and the surname matches or is a variant, then they are probably related since the time of the adoption of the surname. If two people match 12/12 or 25/25, and the surname does not match, they are most likely related before the adoption of surnames. (This statement excludes adoption, and extra marital events.) Being related before the adoption of surnames is probably not relevant to those doing family history research, so matches with others of different surnames are ignored. When two people match and share the same surname, they would be related since the time of the adoption of the surname.

Scientifically, the probability that two people are related is the same on a 12 Marker match and a 25 Marker match, 99% probability that they are related. The question then becomes WHEN the relatedness occurred. A 25 Marker match has a smaller window of 1200 years, while the 12 Marker match has a much larger window of 2500 years.

The surname effects the time frame for when they are related. When the surname matches, the time frame is shortened, so the two people are related since the adoption of the surname. From a genealogical perspective, determining the first recorded instance of the surname would put a time frame for the adoption of the surname, even though it could have been used prior to that even, but not recorded or the documents lost or destroyed.

Matches with other surnames can occur for anyone, with any 12 Marker or 25 Marker result, who belong to any Haplogroup. We happen to observe this situation occurring more frequently with those who belong to Haplogroup R1b, since this Haplogroup comprises a large percentage of the European population and their descendents.

Most matches with other surnames are not worth investigating. 12 Marker results, called Haplotypes, began evolving and mutating with the first Humans. The time frame for relatedness is a relevant factor, and surnames establish a time frame.

To better understand the genetic distances related to our members above, go to the following links on the FTDNA website:

For 12 Marker results

For 25 Marker results-

For 37 Marker results-