Understanding Your Results: Are We Related?
Due to the desire to find those to whom we are related, it is easy to look at Y DNA test results and interpret that the people are related, when the degree of relatedness is most likely outside the time frame of genealogy. Surnames are a key element in establishing a genealogy time frame for evaluating results. All of us are related at one point in time, though this is not relevant to our genealogy time frame.
The 12 Marker Y DNA test is an excellent tool to determine those whom are "not" related within a group of people that share the same or similar surname. When 12 Marker Y DNA test results indicate that two people are related, it is important to consider the time frame indicated by the results. The common ancestor for two participants is known as the Most Recent Common Ancestor, or MRCA. The time frame to the MRCA is shown as a range of time, with probabilities. Y DNA testing does not identify the common ancestor, or specify an exact time frame. Instead, the time frame is a range of generations, with a probability of whether the common ancestor occurred within the range. For a 12/12 match, the range of generations for when the common ancestor occurred, is 1 to 62+ generations at a 95% confidence level. An exact end to the range can not be scientifically identified. Having a common surname establishes the end of the range as the time the surname was adopted.
Using a figure of 25 years per generation, the range for the time frame of the MRCA is 25 to 1550 years. Having a common surname reduces that range. Surnames evolved at different times in different countries. If, for example, surnames evolved in your ancestral country in the 1400's, then the range for the time frame of the MRCA would be 25 to 600 years.
The next step to interpreting your results is to look at the probabilities associated with the time frame of the MRCA. Scientists calculated these probabilities, and divided the range of generations into 3 parts, or subsets. These 3 subsets are the generations to the MRCA at a 50% probability, a 90% probability, and a 95% probability. For those who are not familiar with probability, a 50% probability means that half the time the common ancestor would occur before the number of generations specified, and half the time the common ancestor would occur after the number of generations specified. For the 90 and 95% columns in the chart below, these columns mean that 90, or 95%, of the time, the common ancestor occurred within the specified generations.
For a 12/12 match, the chart below shows the number of generations for the common ancestor, and the probability:
Probability: 50 90 95
Generations: 14.5 48 62
As shown in the chart above, a 12/12 match indicates that 90% of the time, the common ancestor occurred within 48 generations. 95% of the time, the common ancestor occurred within 62 generations. 62 generations, using an average of 25 years per generation, is 1550 years. Most likely, surnames were adopted more recently than 1550 years, perhaps 600 years ago. Therefore, the common ancestor occurred since the adoption of surnames, assuming both participants have the same or variant surnames.
If the common ancestor has been identified by family history research, and there is an adequate paper trail, these probabilities aren't significant. The common ancestor has been identified, and the purpose of the Y DNA testing is to confirm the research.
If a common ancestor for participants has not been identified, then the probabilities are important. The chart above covered the probabilities for a 12/12 Match. The chart below covers the probabilities for a 25/25 match:
Probability 50 90 95
Generations 7 23 30.4
As you will notice, the time frames to the common ancestor are significantly shorter for each of the probabilities when a 25 Marker Y DNA test is used. The time frames have roughly been cut in half with a 25 Marker Y DNA test.
When interpreting results from a 12 Marker Y DNA test, one factor to consider is whether the common ancestor has been identified with a paper trail. If there is a paper trail from both participants to the common ancestor, you have identified the common ancestor. The 12 Marker test may be sufficient, in this case, to confirm the family history research.
A word of caution is necessary. The words "documented research" have many interpretations. The participants may have made up their family tree off the Internet, and call it documented. Even precise dates and locations, which infer some level of research, can be misleading. The author of this article was recently reviewing a pedigree submitted by a participant. The "documented" family tree went to the 1700's, with precise locations and dates for births, marriages, and deaths. The author validated the research for the period 1855 to present. The family had immigrated to the US in 1855. Validating the research in the ancestral country required reviewing the parish registers. After reviewing the Parish Registers for the relevant location for the time period of 1773 to 1855, and all the surrounding parishes, not a single event was found!!! There were serious flaws in the research.
It may not be possible for Group Administrators to validate a participant's research, due to time considerations. At the minimum, it is recommended that a random sampling of events are validated. Where the common ancestor is identified, and you are considering that this participant's tree represents a branch of your family tree, you most likely would want to validate all the research for their tree.
A 12 Marker test where the common ancestor is identified may be sufficient to confirm the family history research. If there is any question regarding the research, the 25 or 37 Marker test is recommended.
For Surname Projects where the common ancestor is not identified, it is recommended to upgrade to 25 or 37 Markers for a 10/12, 11/12 or 12/12 match. If the test results belong to Haplogroup R1b, it is "highly" recommended that the participants upgrade to 25 or 37 Markers.
An upgrade to 25 Markers will reduce the time frame for the common ancestor. In addition, an upgrade to 25 Markers for a 12/12 match may also show that the participants are not related in a genealogical time period. A 12/12 match could become, for example, a 19/25 match.
A 25 Marker and 37 Marker Y DNA test provides a shorter time frame to the MRCA for matches and near matches. It is recommended that Group Administrators encourage participants to upgrade to a 25 or 37 Marker test as necessary. Starting with a 25 Marker test costs a little more, but is a little less expensive than later upgrading.
The chart below shows the probabilities and generations:
Probability 50% 90% 95%
12/12 Match 14.5 48 62
11/12 Match 36.5 84.7 103.4
25/25 Match 7 23 30.4
24/25 Match 18 41 52