More Frequently Asked Questions
- If I submit a sample to you for testing and you find that I match exactly with another person, how many generations ago did we have a common ancestor?
Here are the times back to the MRCA when ALL the markers match.
For example, with 25/25 (all 25 markers match), there is a 50% probability that the MRCA was no longer than 8.3 generations, and a 90% probability that the MRCA was within the last 37.4 generations.
Compare these with 12 and 6 -- with 12 markers, there is a 50% probability that the MRCA was within the last 14.5 generations, while with 6 markers, there is a 50% probability that the MRCA was within the last 29 generations.
Table 1. Probability for Most Recent Common Ancestor (MRCA)
Number of matching markers 50% probability that the MRCA was no longer than this number of generations 90% probability that the MRCA was no longer than this number of generations 95% probability that the MRCA was no longer than this number of generations 6 of 6 29 96 125 12 of 12 14.5 48 62 21 of 21 8.3 27.4 35.7
FamilyTreeDNA's 25 marker test points to a much lower number of generations to the most recent common ancestor than other commercially available tests. We use exacting statistics appropriate for the non-independent transfer of genetic material on the Y Chromosome.Table 2. Examples of previously tested individuals.
Situation Control Code Locus # Result 1 2 3 4 5 6 7 8 9 10 11 California-Same Surname GbG24 1 4 4 2 5 6 0 5 5 4 6 11/11 Match A Match Argentina-Same Surname GbG23 1 4 4 2 5 6 0 5 5 4 6 11/11 Match A Confirmed Family from Germany GbG6 2 7 5 2 2 5 1 2 4 4 5 9/11 **Note Random Family from Galicia GbG13 2 7 6 2 2 5 1 2 4 4 6 9/11 5 Generations in US GbG14 1 1 5 4 2 4 8 0 6 1 4 11/11 Cohen* Match Family from Russia (1989) GbG12 1 1 5 4 2 4 8 0 6 1 4 11/11 Cohen* Confirmed Houston-Same Surname GbG3 3 4 5 2 4 4 0 1 3 5 4 ***Note No Brazil-Same Surname GbG4 2 7 6 2 3 5 1 2 4 4 4 Match
*Same Surname, heritage thought to be Yisrael.
**These two men were 9/11 and had, according to our Population Geneticist, a MRCA anywhere from a few to 110 generations ago, with the Most Likely Estimate (MLE) of 700-800 years ago, when the Jewish Community was almost entirely in Germany! This is the type of information that Dr. Hammer is looking to use when he examines migration from the West to the East.
***These people shared geography, Surname and presumed they were relatives. They are clearly not related as the numerous mismatched alleles show.
- How the test is performed. Do you make DNA fragments from the buccal smear DNA of the two individuals being assessed for a possible relationship and do you analyse the size of the fragments by gel electrophoresis?
Total Genomic DNA is extracted from the buccal swab using an organic extraction followed by an alcohol/ salt precipitation. The DNA is then quantified and a working stock of standard concentration is prepared. The microsatellite loci are then amplified (using PCR). The microsatellite PCR products are then scored for size using polyacrylamide gel electrophoresis. The data from the gels are collected by a computer that reads the gels with a laser. The computer is then able to calculate the size of the microsatellite bands by comparison to a size standard that is run in each lane with every sample. The computer is then able to calculate which alleles are present for each of the loci. The results are then checked by hand to assure that there were no abnormal readings. Multiple control samples are run on each gel to assure that the system is functioning properly.