Family Defining Y-DNA STRs




Two weeks ago, I addressed the formulation of a plausible family tree that would connect the three genetically related Owston/Ouston families.  Twenty-eight Y-DNA subjects have tested in the project to date. Their delineation by family is listed below:

Ganton Family – 4 tested / 4 matching

Sherburn Family (not including the Cobourg Line) – 12 tested / 7 matching

Cobourg Line – 7 tested / 6 matching

Thornholme Family – 5 tested / 3 matching

With 20 matching individuals, we were also able to determine that certain lines had distinctive short tandem repeat (STR) values.


In Y-DNA analysis, an STR or short tandem repeat is a string of two or more nucleotides that repeat in a sequence. It is important to note that STRs are generally found within the non-coding region of the Y-chromosome and they have no bearing on an individual’s health or traits.  The loci of specific STRs on the Y-chromosome are generally designated as DYS for DNA Y chromosome Segment number.

To illustrate how STRs are measured, DYS455 has the following nucleotide string:  AAAT.  The sequence contains three nucleobases of adenine and one of thymine. Depending on haplogroup designations, this particular marker has been observed to range from 8 to 12 repeats.  DYS455 appears to be a very stable STR for men within the I1 haplogroup, as the value of 8 is found in every one of the 5,700 participants in the I1 yDNA Haplogroup Project at Family Tree DNA.  By comparison, the R1b and G2a participants in the Owston/Ouston project all have 11 repeats.

With any STR, mutations occur with a loss or gain of repeats on a particular marker.  Many times these are single sequence losses, but multiples can and do occur.  By using different color text for each sequence, the number of repeats using DYS455 as an example would look as follows:repeats

While the chemical sequence is the same for every man, the number of repeats is variable.  Since men descending from a common male ancestor have nearly identical results over several markers, it is valuable for surname studies. Because men sharing the same haplogroup can be related thousands of years in the past, increasing one’s testing resolution will narrow the number of individuals who happen to share a common ancestor in more recent centuries.


By comparing the various STRs among those matching in the Owston/Ouston DNA project, we are able to determine the clan’s modal haplotype at 111 markers.  The Owston/Ouston modal haplotype can be found here.

Of the 20 matching participants, there were some mutations that are distinct to a family, branch, or even a specific line.  In two cases, these mutations can be traced to specific individuals.  These defining STRs are illustrated in the same chart that was used in last week’s post.  It is repeated below.



The Owston/Ouston family has been placed in the I-Y1843 haplogroup – a subclade of the I1 haplogroup.  Since so few people have tested with the Y1843 mutation or its phylogenetic equivalents, a modal haplotype for I-Y1843 is not currently known.  By going upstream to the next SNP (Single-Nucleotide Polymorphism) mutation of I-F2642 and determining its modal haplotype, it is possible to see differences between F2642 and the Owston/Ouston family.  A comparison of the F2642 modal and the Owston/Ouston modal is found here, while the specific differences in 12 non-matching STRs are as follows:



YFull estimates that the F2642 mutation occurred 4100 years in the past and that all individuals sharing this mutation have a common ancestor who lived 3500 years ago.  Our family modal is a genetic distance (GD) of 14 from the F2642 modal.  All losses and gains of repeats are added together for this computation; however, multi-copy marker difference (as in CDY), are treated as one genetic distance.  The Owston/Ouston modal haplotype occurred more recently and this could be calculated, as each STR has its own mutation rate.  Therefore, the Owston/Ouston modal haplotype may have appeared several hundred years before the development of our surname.  I plan to revisit this in the future.


It appears that a large portion of the Ganton family may carry the modal haplotype, as this is confirmed among three members of the line.  Ganton02, who was from the Rillington Builder line, exhibited two mutations at 43 markers.  It will be necessary to test others to determine if these mutations (and others which may be found at the 111 level) are distinct to a person, a small family group (we call a segment), or for the entire line.  In addition, Cobourg08 has the modal haplogroup.  This anomaly will be discussed below.


A reduction of one repeat on DYS481 is indicative of the entire Thornholme family.  All three matching members have 25 repeats rather than 26 as found in the modal results.  It is impossible to trace this to any single individual, but since it appears in two branches (the Michael Owston branch and the William Owston branch), the mutation occurred with Richard Owston (d. 1739) or in the subsequent three generations.


The mutation of DYS650 at 18 repeats (as opposed to 19) can be traced to Thomas Owston (1627-1681) and is found in his descendants in the Thorpe Bassett and Holderness branches of the Sherburn family. Since it is missing from his brother George’s descendants, the mutation can be specifically traced to Thomas.


In addition, Thomas’ son Peter (1661-1699) is a source of a mutation as well.  A loss of a repeat on DYS442 (normally 12) is a defining mutation found within the Thorpe Basset Branch of the Sherburn family.  Since 11 repeats appeared in descendants of Peter’s two sons but not in his brothers’ descendants in the Holderness branch, it can be attributed to Peter Owston.  This particular scenario is further discussed at the Lineal Arboretum.  The markers represented in this older blog post are based on GeneTree’s calculation of 16 and 17 and not FTDNA’s calculation of the same mutations as 11 and 12. FTNDA differed from other companies (GeneTree, Ancestry, and SMGF) on how the repeats were counted on several STRs including DYS442.


Eleven repeats instead of 12 at DYS643 manifests in all Cobourg line participants except one (this will be explained below).  Since relatives up to the fourth cousin, once removed level share this mutation, it is safe to assume this is an identifying marker of this line.  This mutation’s origins could have occurred within a four generation span between and including John Owston (1666-1735) and William Owston (1778-1857).  This one marker’s deviation separates the Cobourg line from the modal haplotype.


The Toronto line can be identified by 12 repeats, as opposed to 13, on DYS446.  This mutation could have entered the line at anytime between 1714 and 1877 – a six generation span.  This may have been an identifying marker for the Michael Owston branch; however, since the Toronto line is the only extant line of this branch, this cannot be confirmed.  The Owston surname and Y-DNA in four other lines in this branch has ceased during the last 75 years.  These surname extinct lines included the Dansville, NY line (1943), the Pickering line (1960), the Pirbright, Surrey line (1994), and the Harpham line (2001).  The years represent the death of each line’s last male Owston.


There is at least one identified back mutation, as Cobourg08 has 12 repeats on DYS643 rather than 11 – which is indicative of this line.  This back mutation could have occurred within period of five generations beginning with James Wilson Owston (1808-1858) until the birth of Cobourg08.  Dating this back mutation could be narrowed if further testing occurs, as Cobourg08 has two second cousins, twice removed in a parallel segment; however, neither shares our common surname, as their grandfather changed his name to match that of his step-father’s.


In addition, several parallel mutations have been observed among our participants. This occurs when a mutation shows up in at least two people independently of each other.  Ninth cousins, once removed Cobourg06 and Sherburn09 both have 20 repeats on DYS570.

Three participants carry 11 repeats, as opposed to 12, on DYS556. This mutation is found in the results for Sherburn08, Sherburn09, and Thornholme05.  The two Sherburn family members are from different branches and are ninth cousins, once removed.  Thornholme05 is respectively a twelfth cousin, once removed and a twelfth cousin, twice removed to the two Sherburn participants.

Close relatives of these individuals do not share these mutations  and they may very well be private occurrences.


While we are confident that we have identified five identifying STRs, there may be others that further testing may discover.  In some cases, we may not be able to determine if a recorded STR mutation is indicative of the line or of an individual.  This is due to the lack of diversity in some families as discussed in the former post.  While we strive to test more individuals and take some of our remaining matches to 111 markers, we may discover further identifying STRs.

In addition to STR testing, the Owston/Ouston DNA Project has moved into the realm of Next Generation Sequencing with FTDNA’s BigY test.  This particular test studies Single-Nucleotide Polymorphisms or SNPs, which are commonly called SNiPs.  SNP mutations determine haplogroups, but the BigY reports novel SNPs as well, which may be indicative of family branches

We currently have four subjects who have tested with the BigY:  Cobourg01, Ganton04, Sherburn08, and Thornholme04.  We hope to add a fifth individual, Sherburn12, during this year.  Others will be added as needed and as funds permit.  Currently, all four participants’ results are being analyzed by YFull. The analysis of first three participants should be available within several weeks. Our fourth participant’s results are scheduled for late July.  Like STRs, the novel SNP variants found among our family members should be defining markers for specific family branches and we hope the results can answer several unanswered questions concerning how our families are related.


I1 yDNA Haplogroup Project. (2016). Retrieved from

I1 Z140 YDNA Project. (2016). Retrieved from

Owston, J. (2012, April 14). Tying a Y-DNA mutation to a specific ancestor. Lineal Arboretum. Retrieved from

Owston, J. (2012, December 12). A new Y-DNA mutation found in the Owston/Ouston family. Owston/Ouston One Named Study.

Owston, J. (2016). Owston modal haplotype compared to the I-F2642 modal haplotype. Retrieved from

Owston, J. (2016, May 26).  Generating a plausible family tree. Owston/Ouston One Named Study. Retrieved from

Owston/Ouston DNA Project (2016).  Retrieved from

YFull. (2016).  YFull YTree v 4.05. Retrieved from

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