MITOCHONDRIAL
DNA
Copyright © August 2004, Revised 2006, 2007, 2015
Mary Fern Souder
The mitochondrial DNA (mtDNA)
test examines DNA in the mitochondria of the cells. This analysis examines
entire section of the DNA, protein by protein. DNA is composed of four
chemicals, Adenine, Cytosine, Guanine,
and Thymine, which are repeated in various patterns.
A size-comparison
of mitochondrial DNA vs. the Y-chromosome (which is tested for men), is that
the mitochondria is the size of a little town, and the Y-chromosome is long
enough to reach across the United States. Thus, only certain spots or
"snippets" of the Y-chromosome are tested for men, whereas, an entire
block of the mitochondrion is analyzed.
The mitochondrion
was first sequenced in 1981 in England at Cambridge University, and the sample
used was that of one of the English scientists.
The results of this person's analysis were known as the Cambridge Reference Sequence (CRS), and
the CRS become the world standard for comparison of all subsequent persons who
did mtDNA testing. Any value which
differed from this standard was designated a mutation. This obviously was
an artificial standard, but nonetheless served as the benchmark (with slight
modifications known as the Revised
Cambridge Reference Sequence (RCRS), against which all others were compared for
the next 31 years.
However, after a
reassessment of a much larger and globally diverse population, in 2012 Dr. Doron Behar
and his team of scientists published the Reconstructed
Sapiens Reference Sequence
(RSRS). Use of this standard has
resulted in those of Western European descent showing more mutations than when
previously compared to the British scientist.
The RSRS is now (at least until 2015) the standard against which all
worldwide mtDNA results are compared. To accommodate those who did early mtDNA testing, FTDNA provides two sets of results so that
participants can see both their old RCRS and their new RSRS results. Regardless
of which sequencing model is used, a person’s matches will be to the same
identical persons (who also will be able to see their results using both
models.
Due to the huge expenditure of time that would be required
for reprogramming and replacing CRS results with RSPS in this study, this
procedure will not be undertaken. Anyone
who matches the RSPS results of any participants in this study will be sent an
automatic notice of their match.
There are three
components to mtDNA testing: Hypervariable Region 1 (HVR1) containing 569 base pairs, Hypervariable Region 2 (HVR2) containing
574 base pairs, and the Coding Region.
The results of all three tests are known as the Full Mitochondrial Sequence (FMS). Mutations which occur are either
a substitution in the sequence, an insertion in the sequence, or a deletion in the sequence. A few of the participants in this family
study have upgraded to the FMS, but most have not.
MtDNA is passed from a mother to all of her children of
both genders. The mother and child will have an identical mtDNA
sequence except for some rarely occurring mutations. Therefore people who can
trace their ancestry back through an unbroken string of female predecessors to
a common female ancestor will have identical or very similar mtDNA sequence.
Because I believe
that our maternal ancestors are equally as important as our male ancestors,
participants who carry the mtDNA of our remote
grandmothers have been included in this study. The mtDNA
contributed by some of the participants was of a very common type, and have
numerous matches in the ftDNA database. Others,
however, seem to be much less common, and have no perfect matches at this
point.
Studies have
emerged which track the various mitochondrial haplogroups (or clades) to
geographic regions. Haplogroups are also associated with racial identity.
Caucasian haplogroups include U, H, K, N, T, I, J, X, V, and W. Native American
Indian haplogroups include A, B, C, D, and X. Asian haplogroups include A, B,
C, D, and M. African haplogroups include L1, L2, and L3, and M.
Haplogroup H is the most common mtDNA haplogroup in Europe, where up to 48% of all women fall
into this category. Participants who have tested their Full Mitochondrial
Sequence will have a more definitive result, eg. H5a1 as compared to H5, or K1c2 as compared to K1.
I was especially pleased
that results of mtDNA testing for four of our early
female ancestors established a missing link between them and a suspected
earlier ancestral line. These women were
Catherine Fine, Catherine Johnson, Margaret Mashburn,
and Rhoda Strain. In each case, the women were closely associated with another
woman who carried the same maiden name and who did have a documented paper
trail back to an earlier lineage.
As you click on
the link for each of the mtDNA lineages presented
below, you will see how many maternal matches have been reported to
FamilyTreeDNA for each individual as of October 2015, after 14 years of
testing. The number of matches is reported only in order to give an idea of the
frequency that this unique mtDNA signature appeared
in the FTDNA database as of 2015, and due to time restraints I will not
continually update the number of matches.
If you think that you may be a member of our family and would like to contribute an mtDNA sample, you may obtain a kit at the following FTDNA site: FTDNA.
Last Updated on 10/9/2015
By Wallace W. Souder