Time To Most Recent Common Ancestor.
The chief purpose of DNA studies is to rule out those who are not related within the time span of surname usage, to identify those who are, and how recent or close that connection is. This can direct our researches to certain family groups and regional localities. This is chiefly by comparing marker to marker and looking at numbers and distances of mutations.
What Does it Mean?
Mutations occur at random. This means it is possible for two distant cousins to match exactly on all markers while two brothers might not match exactly. Because of the random nature of mutations we must use statistics and probability to estimate the Time to the Most Recent Common Ancestor (TMRCA). The actual calculations of TMRCA are mathematically complex and depend on knowing the rate of mutation and the true number of mutations.
Based on certain assumptions we derive the probability tables below.
| 25 Markers | ||||||
| The probability that two participants share a common ancestor when matching on "X" number of markers within the last "Y" generations. | ||||||
| Marker Matches |
4 Generations |
8 Generations |
12 Generations |
16 Generations |
20 Generations |
24 Generations |
| (100 Years) | (200 Years) | (300 Years) | (400 Years) | (500 Years) | (600 Years) | |
| 25 of 25 | 61.17% | 84.92% | 94.15% | 97.73% | 99.12% | 99.66% |
| 24 of 25 | 25.5 - 28.0% | 55.3 - 58.8% | 75.6 - 78.8% | 87.4 - 89.7% | 93.7 - 95.2% | 96.9 - 97.8% |
| 23 of 25 | 7.0 - 8.5% | 26.4 - 30.6% | 48.6 - 54.2% | 67.0 - 72.4% | 80.1 - 84.5% | 88.5 - 91.7% |
| 22 of 25 | 1.3 - 1.9% | 9.5 - 12.0% | 24.6 - 29.7% | 42.4 - 49.1% | 58.9 - 65.9% | 72.3 - 78.5% |
| 21 of 25 | 0.2 - 0.3% | 2.6 - 3.3% | 9.8 - 12.0% | 21.7 - 25.6% | 36.1 - 41.5% | 50.8 - 56.7% |
| This
tables
show a range of probabilities based on the Family Tree DNA Time Predictor.
The FTDNATiP™ results are based on the mutation rate study presented during
the 1st International Conference on Genetic Genealogy, on Oct. 30, 2004 and take
into consideration the mutation rates for each individual marker being compared.
* Note this is contentious. Some say
the figures should be multiplied by one and a half to two and a half times.
The ranges were developed based on data from the Blair DNA Project. These ranges could possibly expand if data from other surname projects were considered. The above probabilities assume that the participants have NO prior knowledge of how they might be related. |
||||||
| 37 Markers | ||||||
| The probability that two participants share a common ancestor when matching on "X" number of markers within the last "Y" generations. | ||||||
| Marker Matches |
4 Generations |
8 Generations |
12 Generations |
16 Generations |
20 Generations |
24 Generations |
| (100 Years) | (200 Years) | (300 Years) | (400 Years) | (500 Years) | (600 Years) | |
| 37 of 37 | 83.49% | 97.28% | 99.55% | 99.93% | 99.99% | 100% |
| 36 of 37 | 58.6 - 59.2% | 88.8 - 89.2% | 97.4 - 95.6% | 99.4 - 99.5% | 99.8 - 99.9% | 99.9% |
| 35 of 37 | 29.3 - 32.3% | 69.2 - 72.8% | 89.4 - 91.5% | 96.8 - 97.7% | 99.1 - 99.5% | 99.8 - 99.9% |
| 34 of 37 | 10.3 - 13.5% | 42.9 - 50.5% | 72.2 - 79.1% | 88.6 - 92.7% | 95.8 - 97.8% | 98.5 - 99.4% |
| 33 of 37 | 3.3 - 4.1% | 24.0 - 28.0% | 53.6 - 59.2% | 76.6 - 81.2% | 89.7 - 92.6% | 95.9 - 97.4% |
| 32 of 37 | 0.9 - 1.2% | 11.4 - 14.0% | 35.2 - 40.5% | 60.8 - 66.7% | 79.7 - 84.2% | 90.6 - 93.4% |
| 31 of 37 | 0.1 - 0.3% | 4.3 - 6.1% | 19.0 - 24.6% | 41.7 - 49.9% | 63.8 - 71.9% | 80.1 - 86.3% |
| 30 of 37 | 0.0 - 0.1% | 1.5 - 2.4% | 9.6 - 13.4% | 26.7 - 34.3% | 48.1 - 57.5% | 67.5 - 76.1% |
| 29 of 37 | 0.00- 0.01% | 0.3 - 0.5% | 3.0 - 4.4% | 11.5 - 15.5% | 26.4 - 33.3% | 44.6 - 53.2% |
As you can see from the above table more markers reduce the number of generations to TMRCA. The Chart below shows how increasing the number of markers tested, decreases the number of generation to TMRCA when all markers match.