October 2019
by Ed Ralston
The following chart shows FTDNA STR mismatches or mutations for all R-M269 (R-BY15421) matching members of the Ralston Project:
The purpose of this analysis is to develop a hypothetical tree for each member to the most recent common ancestor of the group (MRCA). Where genealogical data falls short, assumptions based on y-DNA are used to fill in the gaps as much as possible.
The criteria used for this prediction is the assumption that where mutations have occurred and this mutation value is shared by other members (values in red above), that It is more likely that these mutations occurred in as few mutation events as possible. For example, if four members share the same mismatch value on an STR, it is less likely these occurred as four separate mutation events, coincidentally to the same value. It would be more likely that this happened in one or two events, in common ancestors, and the values passed down to the members. This new value is the “signature”, or part of a signature, of that common ancestor.
Where a presumed signature is precluded by another presumed signature on a different marker, the marker that has the slower mutation rate is given precedence. For example, DYS449 and CDYa have values shared by three members, both sets including A Ralston. If the values in both cases came from a common ancestor, it would require back-mutations of one of the others in one or the other STR, back to the original value. Since the probability of that is very low, it is assumed that one or the other STR mutations is the result of more than one event. In this case, since CDYa mutates about twice as fast as DYS449, it would be more likely that multiple mutation events occurred on CDYa.
The following hypothetical tree is based primarily on this assumption. The tree is similar in form to the trees generated by Dave Vance’s SAPP tool at jdvtools.com, though, by adjusting signature sensitivity (pfactor) the SAPP tree results are also similar. Mutations are shown as they are assumed to have happened in the lineages.
SHARED MISMATCHES to MODE
DSY449: 29 to 30 – This marker is in the 1-37 range at FTDNA. Although it is listed as one of the faster mutating markers, statistics show it to only mutate on an average of once every 120 generations – about every 3,000 years [1]. There are two mutations on this marker, all from 29 to 30, by the following:
A Ralston 534344
J Ralston U2178
The conclusion is that these two may have shared a common ancestor more recent than the MRCA that passed the 30 value to them.
CDYa: 37 to 38 – This marker is in the 1-37 range at FTDNA. It is one of the multi-copy markers. Some consider CDY to be the fastest mutating marker. Even so, it only mutates on average every 61 generations, or about every 1,525 years. This mutation is shared by:
B Ralston 380316
A Ralston 534344
There are two possibilities: These mutations were coincidental (convergent) or from a common ancestor. If B Ralston and A Ralston inherited the 38 value from a common ancestor, then they would share that more recent common ancestor with J Ralston above. This would require that either J Ralston had a back mutation on DYS449 to match A Ralston, or the A Ralston had a back mutation on CDYa. Convergent mutations on CDYa are more likely than back mutations, so this is considered as just coincidental.
CDYb: 40 to 41 – see CDYa above.
M D Ralston 261127
L R Ralston 913186
The conclusion is that these two may have shared a common ancestor more recent than the MRCA that passed the 30 value to them. There are genealogical records to also suggest this.
DSY520: 20 to 21 – This marker is in the 38-67 range at FTDNA. It is a relatively slow mutating marker, mutating on average of once every 549 generations – about every 13,725 years. So, sharing a mismatch on this marker is even more suggestive of a common ancestor. It is shared by:
P A Ralston IN50749
R W Ralston 874798
The conclusion is that these two may have shared a common ancestor more recent than the MRCA that passed the 30 value to them. There are genealogical records to also suggest this.
ESTIMATED GENERATIONS
The are several resources that estimate time or generations to the MRCA (based on genetic distance or actual STR values), which produce varied results. This can depend on the algorithm used or the mutation rate data.
Below is a table from several sources, showing the greatest distance in generations between any two individuals in this group, ranging from 8 to 15, and averaging around 12:
| FTDNA TiP | 9.5 | |
| McDonald | 15.0 | |
| Nordtvedt 67 | 8.0 | |
| McGee | 15.0 | |
| Average | 11.9 |
(1] All mutations rates are based on work of Marko Heinila, Helsinki University of Technology, Unpublished, 2012