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X Marks the Spot

Roberta Estes

When using autosomal DNA, the X chromosome is a powerful tool with special inheritance properties.  Many people think that mitochondrial DNA is the same as the X chromosome.  It’s not.

Mitochondrial DNA is inherited maternally, only.  This means that mothers give their mitochondrial DNA to all of their children, but only the females pass it on.  So tracking mitochondrial DNA back up your tree, it goes to your mother, to her mother, to her mother, until you run out of direct line mothers on that branch.  The mitochondrial DNA is shown by the red shading below.  The Y chromosome is blue.

Mitochondrial DNA is not one of the 23 chromosomes you obtain from both of your parents.

The X chromosome is different.  The X chromosome is one of the 23 pairs of chromosomes.  The 23rd pair is the pair that dictates the gender of the child.  If a child has an X and a Y, it’s a male.  Remember that the father contributes the Y chromosome to male children only.  If the child has two X chromosomes, it’s a female.

The inheritance patterns for the X chromosome for males and females is therefore different.  Men inherit only one X chromosome, from their mother, while women inherit two Xs, one from their mother and one from their father.  In turn, their parents inherited their X in a specific way as well.  All ancestors don’t contribute to the X chromosome.

In my paper published in the Journal of Genetic Genealogy (Vol. 6 #1) in the fall of 2010, in a paper titled Revealing American Indian and Minority Heritage Using Y-line, Mitochondrial, Autosomal and X Chromosomal Testing Data Combined with Pedigree Analysis, in addition to other types of analysis, I analyzed my X chromosome and what it told me about where some of my Native and African inheritance came from.

At that time, the only company returning ethnicity information about the X chromosome was deCode genetics.  My X chromosome showed that I carried Native American heritage on the X chromosome as well as on some other chromosomes.

I’m going to share the part of this paper involving the X chromosome and how it can be used genealogically and in particular, to identify candidates who could have contributed this Native and African ancestry.

Blaine Bettinger granted me permission to use 2 charts in the paper and again for this blog.  Thanks much, Blaine.  He originally published them on his blog, The Genetic Genealogist, in December 2008 and January 2009 in his blogs about how to use the X chromosome for genealogy.

The first chart shown below is the male’s X chromosome inheritance chart.  You can see that he only obtains his X chromosome from his mother who inherited it from both her mother and father, but only from some of her ancestors on either side.

The next chart is the female’s inheritance chart.  She obtains her X from both of her parents.

Blaine color coded these, pink for females and blue for males, so I was then able to quickly use them to fill in my ancestor’s names.  I know this next chart looks messy, but it’s what I did and I still refer to this regularly.  I don’t’ expect you to READ this, I expect you’ll DO something like this with your own pedigree chart.  So excuse the look into my messy closet:)

I numbered the slots so that I could work with them later.

The results were quite surprising.  The first thing that became immediately evident is that I didn’t have to worry about a few lines.  On the chart below, you can see that my mother’s German lines could be immediately eliminated, because we know they were not the source of the Native American heritage.

This leaves only three individuals on the mother’s side as candidates for Native ancestry.  Those are the numbered slots between the German lines.

The people below correspond to the numbered slots above.  See, I told you that you didn’t need to read the chicken scratch chart.

5 – Naby (probably short for Abigail), last name unknown but may be Curtis, born in Connecticut in about 1793.

7 – Capt. Samuel Mitchell, born probably about 1700, possibly in Kittery, Maine or possibly in Europe, mother unknown.  This line is probably eliminated.

8 – Captain Mitchell’s wife, Elizabeth, last name unknown

Using the pedigree chart, we narrowed the mother’s side from 21 possible slots to 5 with one more probably eliminated.  Of these, mitochondrial DNA sampling of the descendants of the two women whose last name is unknown would produce the answer to the question of maternal Native or African ancestry.

The father’s side is more complex because many of his ancestors immigrated in the colonial era.  Candidates for Native ancestry are as follows:

20 – Mary, wife of John Harrold (Herrald, later Harrell), born about 1750, died in 1826 in Wilkes County, NC.  She was rumored to have been Irish.

21 – Michael McDowell, born 1747 in Bedford Co., Va. – his mother is unknown.  His father was a second generation immigrant who lived in Halifax and Bedford Counties in Virginia.

22 – Isabel, wife of Michael McDowell, probably born about 1750, surname unknown, located in Virginia.

27 – Elizabeth, born about 1765, wife of Andrew McKee of Virginia.

28 – Agnes Craven is the last slot on the chart, but not the last in the line.  Her father was Col. Robert Craven born 1696 in Delaware and was well to do.  His mother is unknown.  Robert’s wife was Mary Harrison, born in Oyster Bay, New York to Isaiah Harrison and Elizabeth Wright.  These lines appear to reach back to Europe but are unconfirmed, probably eliminating these lines.

30 – Phoebe McMahon, wife of Joseph Workman, born 1745 York Co., Pa, daughter of Hugh McMahon, mother unknown.

31 – Gideon Faires’ mother was Deborah, born 1734, possibly in Augusta Co., Va.

32 – Sarah McSpadden’s father was Thomas McSpadden born 1721 in Ireland, eliminating this line.  Sarah’s mother was Dorothy Edmiston whose father was born in Ireland, eliminating that line.  Dorothy’s mother was named Jean and was born in 1696 but nothing further is known.

33 – Martha McCamm, born before 1743, wife of Andrew Mackie of Virginia, parents unknown.

On the father’s side, we began with 13 slots, positively eliminating one and probably eliminating a second, leaving 11.  Of these, 7 could be resolved on the maternal line by mitochondrial DNA testing.  Taken together, this side of the pedigree chart is a much better candidate for both Native and African DNA sources.  Notice all of the females who have no surnames.  These are excellent places to look for Native ancestry.  On my chicken scratch version, these are highlighted in yellow.

While the X chromosomal pedigree chart analysis is not the perfect scenario, the pedigree chart has 128 slots.  Using the X chromosome narrows the candidates to 34 slots.  Genealogy narrowed the slots to 15 and focused mitochondrial DNA testing could narrow them to 6.  Further genealogy research on those ancestors could potentially eliminate them by placing them “over the pond” or by discoveries which would facilitate DNA testing.

Marja and Me

You might recall that Marja and I are also related on our X chromosome.  In this case, since she is from Finland, the probabilities are exactly the opposite.  It’s much less likely that our connection is on my father’s or mother’s British Isles lines, and much more probable that it’s through my mother’s German lines. The early colonial settlers tended to be from the British Isles and certainly the people filling the X chromosome slots from my father’s side appear to be, with names like McDowell, McSpadden, etc.

Mother’s Anabaptist line (Brethren) is the German grouping through my mother’s father and descends from France and Switzerland,although these particiular lines don’t appear to have become Brethren until after immigrating to America.  Marja also has other matches with people from the Anabaptist project.

Those end-of-line people are:

Mother’s Dutch line is eliminated, because it’s through her father’s father.  Marja and I thought that might be a possibility, but we can see from this chart that it is not.  My father also has a Dutch line that was eliminated because it came from his paternal line.

Mother’s Lutheran Palatinate line, end-of-line ancestors show below, is though Mother’s maternal line.

Note that the mitochondrial line is indeed one of the lines that contributes to the X chromsome inheritance path, but only one of many.

So Marja, it looks like we have to be related through one of my British Isles ancestors, listed in the first part of this article, or from one of Mother’s two German groups.  Personally, I’m betting on the German groups, but you never know.  DNA is full of surprises.

The good news is that my mother’s information is also at GedMatch, along with mine and Marja’s, so by process of elimination, we can at least figure out whether to focus on the pink or the blue side of my chart.

Today, downloading your raw results to GedMatch, combined with Blaine’s X charts above, is really the only good way of working with X chromosome matches.

I’m planning to package this article as a pdf file and send it to my X chromosome matches.  You can substitute your information for mine and do the same thing.  Hopefully, your matches will then understand the X chromsome, its unique inheritance properties, and will provide their X end-of-line ancestors for you as well.

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