the castle of Iníon Dubh, where I first located the trail of my McCain family |
Y Chromosome DNA In Genetic Genealogy
This is a brief introduction on Genetic Genealogy using the Y chromosome. The Y chromosome (Y-DNA) is passed from father
to son only, in a direct male line, and this makes it the best test for surname
studies. A Y-DNA test is for men only. Women do not carry the Y chromosome. Women use a male proxy in the line they are researching to obtain a Y-DNA sample. Men who are researching a non direct paternal line must also use a male proxy from the line they are researching.
There are two types of tests used with
Y-DNA. There is a STR (short tandem
repeat) test and a SNP (single nucleotide polymorphism) test. STR
tests are used to find genetic matches in a direct paternal line. These matches can be recent to distant. With a company like Family Tree
DNA Ltd, this test comes in the form of a 11, 25, 37, 64, or 111 loci test. Most participants use the 64 or 111 level as
it provides more data. The STR test will
easily locate a paternal DNA match and give an estimate of the time to the most recent common male ancestor.
One aspect of a Y-DNA STR test is
that it allows you to confirm kinship to lines that you have no paper records
to show a connection. This allows the Y-DNA participant to use primary source records to all the families in his
match group. A family may have branches they
did not even know of prior to testing.
As these matched families collect their data, a much better history of
the family is revealed. One letter from one family, one note on a census record, etc., can allow all the matched
families to use the data with complete confidence.
A wet day in County West Meath just prior to a Bean Sí incident |
However, STR matches can have some issues in
analysis. Some STR loci will mutate back
to, or close to, their original position.
This means two branches in a family may appear much closer (in time) to
their most recent common ancestor. This
situation is called ‘convergence.’
Conversely, if Joe sat under a UFO one night, he might have one STR mutation that shows a great distance to a shared common male ancestor, even to the point of Joe not being listed as a match at the lower level test. At the higher level test, we can see Joe is a match. Poor ole Joe just had a unique mutation on that one STR locus. I have seen this happen several times in my consultant work. The issue is one STR locus mutated a greater distance than is normal. This is why the higher level STR tests are recommended.
In the early days of genetic testing, SNPs were
dated thousands of years ago and showed basic ethnic and tribal connections. In the past few years SNP testing
has advanced greatly. Many new SNPs have
been discovered and the number is growing. The new SNPs are younger in age and provide data that can be used in genetic
genealogy. SNPs are more stable than STRs. The mutations are permanent and take place at a stable rate. SNPs provide a method to expand on your STR test and match group and resolve any issues that come up.
The data
is becoming so detailed that the SNPs can differentiate between individual
branches in a family. So, even when
there are no primary sources available, an advanced SNP test can ascertain how
two branches of a family are related and locate the geographic point of
origin. As you explore down the SNP path, downstream to newer SNPs, you may find a SNP unique to one line in a family. For example: this will allow you to tell the difference between a branch in a family from Porthall, Donegal, to a related branch in Corbally, north County Antrim. Alas, with SNP test at this
level, you had best bring your cheque book as the path can be a long one, but it is the ultimate tool for the
genetic genealogist.
R1b Y-DNA Haplogroup |
I work in the geographic area of the north of Ireland
and western Scotland. This includes the
province of Ulster, the west Highlands and southern Hebrides, and the western
Scottish Lowlands. This population is remarkable homogeneous and many families share distant common ancestors. Irish and Scottish families often benefit
from advanced SNP testing.
A summary: both STRs and SNPs are
used in Y-DNA testing for genetic genealogy. Your Y-DNA test will include your
STR results and matches, and a basic SNP Haplogroup. This Haplogroup will show paternal ethnic origins and pre surname connections. At this point, you will normally do more
advanced SNP tests to discover your downstream (more recent in time) haplogroup. This will allow you to confirm family branches, clan connections, and locate the geographic area associated with your family.
Do you ever assist others in analyzing their genetic genealogy? Family folklore identifies a family migration from Scotland to Ulster and then on to Colonial America, but with no documentation to support it. I have done the FTDNA Y-700 test but am a newbie when it comes to understanding what my Y-STRs and SNPs might reveal.
ReplyDeleteDennis Armstrong