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From: "David Faux" <>
Subject: [DNA] A Genealogical Goldmine - the X Chromosome
Date: Tue, 16 Dec 2008 16:09:35 -0800


List:

Thanks to the pioneering efforts of Anders here, along with the work of Ann
and Kathy, it is like a light just went on over the past few days and I
realized that what I had assumed about inheritance simply did not apply to
the X chromosome. However the good news is that with what I have learned,
it occurs that exploring this chromosome affords a unique opportunity in the
same category as the Y or mtDNA (and perhaps even greater in the richness of
the finds).

I would suggest that everyone list the potential "donors" to their X
chromosome. I will use the example of myself since I have just completed
this eye opening exercise by looking at my own family. Let me start with
the most recent revelations.

First, I have four grandaughters. Seriously, I thought that I had made a
roughly 25% contribution to their genomic DNA structure. That turns out to
be false. Just looking at the X chromosome, I did not give any of the
daughters of my two sons my X. They are effectively shut out from this
information rich stretch of DNA. They got their XX from their mothers and
each of my sons, who in turn got their X from their mother (I gave them the
Y). However with my daughter's daughter, the story is entirely different.
My daughter got one of her X chromosomes intact from me via one of my
mother's two recombined X chromsomes. So the chromosome my daughter got
from me was unchanged from what was given to me from my mother. So my half
Korean grandaughter got one of her X chromosomes (recombined via her mother)
and an intact X from her Korean father. So I am more closely related to my
daugher's daughter then to my sons daughters in the biological sense.

Second, it is imperative to trace the X line back to realize that if a male,
you received twice as much X chromosome contribution from your mother's
father's mother's father's mother and so on than you did the mitochondrial
line of mother's mother's mother's mother and so on for the simple reason
that with each male he passes on the chromosome he inherited intact to his
daughter (no crossover and recombination).

It is necessary to realize that in the X line, of your 64 gggg grandparents,
only 13 contributed to your X. Therefore these individuals should be
identified to know who is in and who is out. When I do this I get 10
individuals from the British Isles, two from Germany, and one Six Nations
Mohawk.

Here is where the genealogy comes into play. If you believe you have a
Cherokee ancestor who is a gggg grandparent (rather common tradition among
Colonial American descendants), and this is only an oral tradition, if it is
true then this individual only made a small to non - existant contribution
to your X chromosome. Actually my well documented Mohawk ancestor goes back
9 generations and so technically I am 1 / 256 Mohawk. This individual
contributed .004 to my autosomal structure and so it would be doubtful that
any would be picked up by decodeme or 23andme as it would be "below the
bar". However in my case, the ancestor gave a Mohawk X to her son who gave
it to his daughter (my gggg grandmother) who gave it to her son who gave it
to his daughter and so on to my maternal grandmother. This means that the
.004 on the autosomes goes up to 8% on the X chromosome. That is just the
luck of the draw but if you want to determine if and how much is likely to
have come from any particular ancestor it will be necessary to "do the
math".

I have long been told that the Williamsons are part African (well it was the
"c" word that was used by my grandfather who told me). The phenotype of all
of those in the early generations of the family would be consistent with
this statement (although it could simply be at one end of the European
normal range). Dark skin, black eyes, and curly hair - that was my
grandfather and his mother before him. In doing the genealogy I identified
the only likely candidate (although I guess others are possible). This was
one James Hornsby, born 1784 in Trimdon, Durham, England. He as born just
after the American Revolution was over and many wealthy English returned to
England with their entourage. James Hornsby was listed as a "servant" in
the census records. I can find absolutely no record of him (despite very
intense seaches) prior to his baptism. It turns out that this man is the
individual who made the largest contribution to my X (mother's father's
mother and so on). It may (although I include coincidence here as a high
probability) explain the 8% African that decodeme assigned to my X
chromosome. It is not unusual for Europeans to have a few percentage
points, but 8% is fairly large.

So we are left with a great deal of useful information that can be compared
to the genealogical record. Also we can also see who carries more of our
genetic makeup in recent generations. The markers here can allow us to go
on a quest to verify paper trails or oral traditions or obtain findings that
can be checked against the paper trail.

I have really just started taking baby steps and it will take a while to get
up to speed (where Anders and Ann are). However for those willing to
venture into this arena there is so much to be learned, and now so many
interested individuals to share the quest with. If you check out what is
going on at dna-forums you will see the tremendous interest in this subject
there - almost all within the last month - it is virtually brand new and
there is a feeling of getting in on the ground floor and discovering facts
that were never suspected or remained hidden or verifying and fleshing out
what is recorded in the documentary sources. I can see this area burgeoning
perhaps beyond mtDNA and possibly even Y DNA within a year. We shall see.

David K. Faux.


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