Based on the most accepted assumptions we derive the cumulative probability table below. This table simply list the number of generations corresponding to the 50%, 90% and 95% probability levels for various numbers of matches.

If all 12 markers match there is a 50% probability that TMRCA is 14 generations or less, a 90% probability that TMRCA is 48 generations or less, and a 95% probability that TMRCA is 62 generations or less. 

If all 25 markers match there is a 50% probability that TMRCA is 7 generations or less, a 90% probability that TMRCA is 20 generations or less, and a 95% probability that TMRCA is 30 generations or less. 

Although I have no data, I doubt that many groups can trace their surname back more that a 1,000 years. I'm sure there are some than can go back farther, but I would guess they are the exception and not the rule. The Blair surname can be traced back approximately 800 years, to between 1165 and 1200. If you assume 25 years per generation, a 1,000 years is 40 generations. If you use 30 years per generation, a 1,000 years is 33 generations.

Using the above range (33 to 40 generations) and the probability table you can see that a 12 for 12 match means there is less than a 90% probability that the MRCA is within the lifetime of the surname. An 11 for 12 match reduces this probability to approximately 50%. A 25 for 25 match means there is greater than a 95% probability that the MRCA is within the lifetime of the surname. A 24 for 25 match is slightly better that 12 for 12 and a 23 for 25 is somewhat better the 11 for 12.

12-Marker vs 25-Marker

There has been a great deal of discussion about 12-Marker vs 25-Marker Y-Chromosome tests. These discussions have centered on the value of the 12-Marker test, matches to other surnames, and 12 for 12 matches that failed when a 25-Marker test was taken. 

I decided to do a study on the 12-Marker vs 25-Marker issue. I examined the results of 4230 participants in 131 different surname projects. The table below is a summary of what I found.

12 Marker Duplications Across Surnames

I was surprised to discover how many unique 12 marker results were shared by different surnames. There were 1534 distinct 12-Marker combinations. 561 of these combinations had multiple participants. Of the 561 with multiple participants, 275 combinations (49%) had multiple surnames.

There were 3257 participants who shared the 561 unique combinations that had multiple participants. 2227 participants (68% of the 3257) shared a 12 marker combination with someone of a different surname. The table below lists the 12 marker combinations shared by 10 or more surnames, sorted by the number of surnames and number of participants sharing the combination.

To view all 271 12-Marker combinations click here

25 Marker Duplications Across Surnames

There were 1061 participants who shared 354 distinct 25-Marker combinations with multiple participants. 51 participants (4.8% of 1061) shared a 25 marker test result with someone with a different surname. There were 17 distinct 25-Marker combinations that had multiple surnames. The table below lists the 25- Marker combinations shared by 2 or more surnames, sorted by Marker Values. The number of surnames and number of participants sharing the combination are also shown. Note the highlighted value which is shared by 5 different surnames.

12 for 12 Matches that Failed the 25-Marker Test 

The second question frequently asked is "How often does a participant match 12 for 12 markers with someone in his surname group, but match less than 23 for 25 on the 25 marker test?

2853 participants took the 25 marker test. 1476 of those who took the 25-Marker test matched someone in their surname group 12 for 12 on the 12-Marker test. 307 of the participants (20.8%) who matched 12 for 12 with someone in their group on the 12-marker test failed to match at least 23 for 25 on the 25-Marker test. Another 75 (5.0%) participants matched at least 23 for 25 on the 25-Marker test but had 3 or more total mutations. There are 68 distinct 12-Marker sets that fell in this category.

Click below to view the table that lists each of 68 12-Marker combination and surname group number involved. 

Distribution of Values

Out of curiosity I decided to analyze the distribution of values for each of the 25 markers examined in this study. The results are listed below:

You may download an adobe version of the distribution tables by CLICKING HERE

It's interesting to note that if you take the most frequent value for each of the markers you get  13-24-14-11-11-14-12-12-12-13-13-29-17-09-10-11-11-25-15-19-29-15-15-17-17. Only one participant in the group studied matches this 25 marker string. 125 participants matched on the 12 marker string. These 125 matches represent 54 different surname groups.