Looking at the number of people reporting a family story of an Indian great grandma on their maternal line, and then looking at the number of mtDNA results * in North America * which show a indigenous mtDNA type, generally shows there is about 10 stories of a distant Native ancestor on the maternal line for every mtDNA result that actually confirms this. On the other hand, there is almost no one getting an mtDNA result showing a maternal line that is indigenous, when they always thought great granny was completely non native....
http://www.kerchner.com/cgi-kerchner/mtdna.cgi
http://www.mitosearch.org/haplosearch_start.asp?uid=
You have to read through a lot to get the picture, as a lot of people are just reporting European results and family history, but if you do, the pattern that emerges is very clear.
The numbers show a lot more stories a gr gr grandma was an Indian than there was gr gr grandma's who actually were Indian - of any tribe.
My own theory is that a lot of people have gr gr gr gr gr aunts or uncles who married someone who was Native and after a few generations that got turned into "someone back there" which people assumed was their own ancestor, when it wasn't.
(edited to add *in North America* as Hispanic people have a much larger percentage of indigenous maternal lines )
A friend of mine and I were talking about this topic once, and apparently she had learned about it in college to some degree. This is what she told me on the topic, which lead me to believe this is not an exact science yet and can not really be trusted as absolute.
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*****note: she did this on a myspace mail box that was using HTML. So
there is mention of bold letter and a chart that do not work on the
format done by Yahoo here*******
The problem with Mitochondrial DNA testing is it doesn't show all of
the markers and possibilities in your own bloodline. These places can
only show matches with people whose DNA they have in their system, so
if you have, say, an unknown or small ethnic group in your background,
one for which they don't have current date to make a match with, it's
not studied further.
For instance, a lot of black people who've used this very tool for
genealogy have gotten results pertaining ONLY to Europe, with no
mention whatsoever of Africa. One man I know of had traced his
genealogy back generations to specific parts of Africa, yet when he
tested his mitochondrial dna, his search ended in Europe and showed no
African origin, which he knew wasn't correct. But that is because of
the mitochondrial DNA.
So, let's say there is a woman, Jane. Jane is daughter of Mark and
Mary. Jane will inherit all of Mary's mitochondrial DNA, but none of
Mark's mother. Mitochondrial DNA is only a part of the mother's
background.
Mark's mother would have passed it on to Mark and his siblings, but if
it's passed on to a male, he doesn't pass it on to his children since
it is carried only in women. You would have your mother's
mitochondrial DNA, but you would not pass it on to your children. A
sister of yours would.
So, if you trace Jane's ancestry through mitochondrial DNA, you are
only tracing one aspect of the many ancestor's she's had.
<a
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target="_blank"><img
src="
http://i299.photobucket.com/albums/mm315/poets4hire/mtdna.jpg"
border="0" alt="Photobucket" /></a>
The people in bold italic are the only ones MtDNA is going to trace.
So now you have genetic information from Mary, Linda, and Sharon who
are Jane's ancestors, but you are missing information from Mark, John,
Ellen, Harry, Larry, Sue, Bill, Amy, Joe, Ally and Martin. And Sharon
is only Jane's great-grandmother. So, in only three generations,
you've not taken in to account eleven people who genetically
contributed to Jane's DNA makeup.
Now, let's say that Larry is Scottish, Sue is Scottish, Bill is Irish,
and Amy is Dutch. Let's say Joe is Black Dutch, Ally is Melungeon, and
Martin is German/Souix. Let's say Sharon is British.
All you are going to know about Jane is the British ancestry. You
won't know about the german, the souix, the melungeon, the black
dutch, the dutch, the irish, or the scottish. Mitochondrial DNA does
not trace that side.
There is patrilineal DNA, but it is even more limited than mtdna,
because it's not passed on to daughters, at all, unlike mtdna which is
passed on to sons, but not their children.
The really is no 'best' to use, but there are DNA tests that are better.
Patrilineal and Matrilineal DNA, if taking into account the chart
above, will still leave out people. I've seen people test both sides
and get different results on both. One in particular showed african
ancestry of a small group that migrated to britain long ago and were
never slaves in the Y-line (patrilineal) , and in the mtdna it showed
both native american and north african ancestry. If the testing was
taken only on one type of test, they would have very different results
and views of where they originated. There are DNA tests that give a
more detailed determination like autosomal testing, but you must
remember that some genes are dominant and some are recessive, and
ancestors often donate unequal portions of their genes to their
offspring. This is why some siblings sharing the same two parents can
look completely different. Not long ago there were twins born to an
interracial couple for the second time, and one was black while the
other was white. This is because they each inherited different
portions of their parents genetics. One grandparent or parent might
donate less than another or more.
So, basically, DNA can prove ancestry beyond a shadow of a doubt (like
if you are related to somebody famous), but it cannot disprove
ancestry beyond a shadow of a doubt (because you will not be able to
measure all contributors to your DNA accurately, and therefore can be
misled about your origins).