DNA Test results for the McMahon Surname Project
It has become apparent that some testers feel that testing for low numbers of markers is adequate once a match has been discovered. This can sometimes be a false promise and it is not always easy to explain.
It's generally true that you can 'see' a relationship at 25 markers if you can distinguish it from all the other dross that testing at this level throws up. 25 marker testing tends to produce lots of false positives which can only be resolved with a greater number of tests. The greater the number of tests, the greater the statistical significance. FTDNA consider a genetic distance (GD) of 2 is the significant limit at 25 markers, 4 at 37, 7 at 67 and 10 at 111. It then depends on which actual markers are different. Say you have a GD of 5 @ 67 markers which is highly significant; if these differences occurred in the first 37 markers, you probably wouldn't see this relationship at 25 or 37 markers (because of FTDNA cut-off points). Consequently, we are encouraging new and existing members to test to 67, and ideally 111, markers. This is the bedrock of your profile and is used in all projects and studies.
Another problem facing testers is the array of tests available which often causes confusion. Projects like this one, which follow patrimonial inheritance, can only use Y-chromosome DNA data. For example, unless you are following matrimonial inheritance for other reasons, testing for mitochondrial DNA is unnecessary.
Next in importance to STR testing (above) is SNP testing to establish your haplotype. From your STR results, FTDNA are able to predict your most likely broad haplotype. This is shown in red and is normally R1b1a2 for most McMahons and corresponds to the evolutionary stage of early Neolithic Europeans. Deep clade or individual SNP testing is needed to establish further evolutionary branching typically to L21+ (R1b1a2a1a1b4) for most McMahons. Many have tested for more recently discovered SNPs which are now being used (where possible) to define the Project sub-categories. Testers who have returned a positive for their category defining SNP are indicated by an * after their surname.
Another cause for concern among some testers is where no matches are found even when testing to 67 markers. This should not be regarded as a negative result. It is common and simply means that your lineage evolved early (and is outside the FTDNA statistical limits), no other distant relatives have tested or you are the only survivor of your lineage to have made it to the 20th century. Sometimes joining other name projects can result in a match.
Over time a fair number of non-McMahon matches have come to light. Some of these are known adopted names while others are suspected of being adopted names. Prior to record keeping (mid 19th c.) fostering sons between chieftains was a common practice which no doubt could have accounted for some switching names and DNA.
Patrick McMahon joined the Project as a Co-administrator in April 2012 and took over full Administrator responsibilities shortly thereafter.
A new layout of categories was issued in May 2012 followed by several updates.
Please do not hesitate to contact us at any time.
Patricia, Bill, Jim and Patrick