Using DNA Results to Find Ancestors
by Larry E. Jordan

Most of you are researching your Jordan ancestors -- trying to document at least one more generation back in the chain. The difficulty is getting past brick walls created by lost, burned or never-existing records of births, deaths, marriages etc. Hopefully our DNA project will help you get past your brick wall. How can that happen?

The simple answer is for you to find a match between your Jordan DNA and that of another Jordan family who has a documeted family tree that preceeds your own documented tree. Then you can focus on the missing link between your family and the family with matching DNA. The DNA results will not tell you who links your tree and that of the family with matching DNA, but it will tell you that your families have a common Jordan male ancestor -- what geneticists call the Most Recent Common Ancestor (MRCA or TMRCA).

Table 1 below shows the accuracy of various test markers in determining the number of generations back for a MRCA for two related individuals. If two people who participate in the project have 12 of 12 markers that are identical (match exactly), then their MRCA is less than 14.4 generations back for them 50% of the time or 288 years on average. If two people who participate in the project have 25 of 25 markers that are identical (match exactly), then their MRCA is less than 7 generations back for them 50% of the time or 140 years on average. Anything less than a 10 out of 12 markers or 23 out of 25 markers between two individuals is not considered a strong match; the two people may be related, but the common ancestor may have been quite a long time ago as you can see in the last column of the table.

The figure assumes you are test participant A, and you want to trace your ancestry back beyond your oldest documented ancestor MRCA1. The first step is to find a male cousin such as B in the figure to participate in the test. (The figure shows a first cousin, but you may want to go to at least a third cousin.) MRCA1 is the most recent common ancestor for the two of you. You (A) and participant B should have DNA that is a perfect 25/25 marker match because of the small number of generations between the two of you and your common ancestor.

After you have proven your DNA matches that of male cousin B, then you are ready to compare your DNA with that of other test participants to find other cousins. In Figure 1, test participant A finds that his DNA is an 24 of 25 marker match with participant C. As illustrated in Table 1, this match means that A and C share most recent common ancestor MRCA2 who probably lived about 350 years ago. If test participant C has a documented ancestry back to MRCA2, then you are in luck. If not, then you at least have another Jordan with whom you can compare research notes as you both search for MRCA2.

The last example in the above figure is the match between A and D. In this case, A finds that he has a 23 of 25 marker match with test participant D. As indicated in Table 1, the 23/25 match indicates A and D are probably related, but it also indicates their most recent common ancestor MRCA3 is farther back in the chain of Jordan males than MRCA2 -- about 570 years. Again, a fully documented ancestry between D and MRCA3 would give you a great area in which to focus your own research. Knowing the deails of MRCA3 and his descendants may help you find the missing links between your own MRCA1 and MRCA3.

As more Jordan males participate in the DNA testing, the number of potential matches for your DNA increases. The more matches you find, the closer you can pin down the MRCAs for you and the matches that you find. Creating an ancestry map like the one in the above figure will help you know when you have identified each MRCA.

Another way to view these numbers and DNA is to look at the number of mutations in markers over a period of generations. If two men are 8th generation descendants from a common ancestor (they had a common ancestor about 140 years ago), there are 7 births down each line to the men tested. With one mutation out of every 500 possible chances, the following would be typical of the test results for these two men:
-  50% of the time a 25 marker test will be identical
-  35% of the time a 25 marker test will show a one step change
-  12% of the time a 25 marker test will show two one step changes
-  3%  of the time a 25 marker test will show three one step changes

Click here to go to the DNA 101: Y-Chromosome Testing page written by John A. Blair that explains DNA, as it pertains to Y-Chromosome testing and genealogy, in layman terms with as little DNA "mumbo jumbo" as possible.

Click here to go to the Family Tree DNA pages that explain the Most Recent Common Ancestor and the above curve in detail. This site also gives you the MRCA curves for 12/12, 11/12, 10/12, 25/25, 24/25, and 23/25 matches.

Click here for the ultimate use of DNA to trace ancestors across Europe.
The trick is to reduce the uncertainty in the determination of that MRCA until you have identified the individual who is the father of both of your family lines. The ideal process starts with a verification of your own family line of DNA by having distant male Jordan cousins take either the 12 marker or 25 marker DNA test. By proving that they both carry the exact same Y chromosome DNA, you have a solid benchmark which you can compare with the results from other Jordan families who do the same.

As you find Jordan families with matching DNA, you must map them to your own family tree and history. The degree to which your DNA matches determines how far back you probably shared a common ancestor. Figure 1 below shows how this works for 25-marker match results. The figure illustrates how you can use the DNA data and documented family history in combination.