Understanding DNA tests, genetic markers, and their application
as a genealogy tool requires advanced degrees across several
disciplines--Genetics, Calculus, Statistics, Social History, Immigration
History.
However, we all can understand the application if we reduce the study down to the basics so
we can read along with what the experts write.
By no means am I an
expert in the field. However, I spent some time getting up to speed after
I submitted my sample and came up with the matches to two living cousins.
Having the results which indicated somebody somewhere in the world matched
me was nice. The question was, “How can I use this new information to
further my search?”
Note, geneticists not genealogists came up with
these descriptions and names.
Terms:
1. Genome: our genetic sequence
2. Mutation: changes in the genome
3. yDNA: the genetic sequence passed down from father to son
4. mtDNA: the genetic sequence passed down from mother to daughter
5. atDNA: all the genetic combinations passed down from all the other ancestors.
6. Loci: different locations along the genetic sequence; commonly referred to as
markers
7. STR: Short Tandem Repeats are markers where there is a high probability for a
mutation; these markers are used by genetics tests to determine relationships
8. SNP: Single-Nucleotide Polymorphisms are markers where there is an extremely
low probability of mutation; these markers are used to determine Haplogroups and
their inherent subclades
9. Allele: genetic information found at a particular marker; the number of
repetitions of a genetic code at one marker; commonly referred to as knots
10. Haplotype: your personal genetic information
11. Haplogroup: a name given to a group of similar genetic sequences. A new
letter marks a major mutation which branches one group off from another. I
am Haplogroup R. My ancestors went from B to F to K to P to R.
12. Subclade: a minor mutation within the Haplogroup. We, the Proto-Celts from the Atlantic Fringe, are R1b
aka Cro-Magnon Man ; R1a are in Central Europe and on the Asian Steppes; R2 went to
Pakistan
and India.
13. MRCA: Most Recent Common Ancestor; statistically how far back you have to go
to find a connection to another person who matches you through a DNA test.
14. TMRCA: Time to Most Recent Common Ancestor expressed in years
or generations.
15: Donor: Me.
Basic Concepts:
1. As the human genome
ages, it changes. At one time every Homo Sapien Sapien (modern people) had the same
genome. The original sequence has been designated Haplogroup A (no
subclades). They lived
in
Africa and never left. And reportedly, are non-extant.
2. As time went by, the genome changed in some people; especially the
folks who migrated out of Africa into the Steppes and then across to
Europe. Note, Haplogroup R is the farthest down the Haplogroup
Chart from A.
3. Evidence for the change is found by counting the “knots” on the DNA
sequence at specific locations (loci/markers).
4. How is this done? Per
the
FTDNA webpage, scientist #1 does a count. Then scientist #2 does a
different count. And scientist #3 does a comparison. If they don’t
match; they start over.
5. DNA tests which have a mutation at a specific SNP are grouped into a
Haplogroup. To be R1b, you must have a mutation at SNP M343.
6. As part of your test results, there will be an estimated Haplogroup which is based on the initial
STR markers found. My Haplogroup is
estimated to be R1b1a2. And, the Haplogroup is posted in red to indicate
is is an estimate.
7. Some people want to find the definitive answer. Another cousin paid to have the Deep SNP test. FTDNA measured all known
SNP mutations
and found one at P312. That means that we are R1b1a2a1a1b.
And, my cousin's Haplogoup is displayed in green.
There is a chart of my family's
genetic history at my DNA
page. The information is copied from the National
Geographic Genographic Project where I am a contributor. As you go
down the DNA Chart, you will find that R1b1 is the group who settled the
British Isles
at the end of the last Ice Age. Effectively, my family branches from the Proto-Bretans of
the Neolithic Period. Our people built Stonehenge. Historical information has yet to be associated with the additional
markers as you move further down the chart
Having obtained your DNA test results, the question is whether or not
there will be a match and what to do with the information when there is.
Analyzing Information from the Match:
1. Using the 37 marker DNA test as the standard, the markers in the
first group (01-12) mutate at the slowest rate (.002), the middle group
(13-25) mutates at a faster rate (.003), the final group (26-37) mutate at
the fastest rate (.004 - .005). Note, these are approximate averages
across the entire group and not a specific rate per marker. These mutation
rates are based on actual family studies where the living donor did not
match the proven ancestor. Imagine someone asking you to do a DNA test and
then getting permission to dig up your famous ancestor to test the corpse.
And, there are three famous studies where that’s exactly what they did.
Note:
The FTDNA Calculator
effectively does the remaining steps for you and provides information for
multiple-step mutations.
2. For a more precise one-step mutation, go to the MRCA
Calculator. Input the number of markers. Input the mutation rate based on
the group where the mutation is found. Calculate for "Generations to MRCA."
Your best answer is the first generation which is equal to or exceeds 50%. The
answer indicates the number of generations up the family tree to the ancestor
you share with your DNA match.
3. Take out your genealogy paper record. Go up
the family tree the associated number of generations. The person on the tree
directly above is, statistically, your Most Recent Common Ancestor.
And,
finding that person is one of the many purposes for this webpage.
Charles E. Lewis
Davenport IA 52802