Jerry Bryan's Web Pages

Bryan DNA Testing

This page is very much a work in progress.  It is hoped that DNA testing can eventually resolve some relationships in the Bryan family.

Of most immediate interest is the father of my seventh great grandfather Cornelius O'Bryan.  According to Irish Settlers in America by Michael J. O'Brien, Cornelius was the son of Brien O'Brien Sr. of County Clare, Ireland.  There is reason to suspect that this is correct, but there is also reason to suspect that this is not correct.

Brien O'Brien Sr. had a son named Brien O'Brien Jr.  It is hoped that by comparing the DNA of descendants of Brien O'Brien Jr. with the descendants of Cornelius O'Bryan that some light might be shed on this issue.

There is also reason to suspect that Cornelius O'Bryan might have been related to Morgan Bryan who married Martha Strode.  It's certainly the case that Cornelius and Morgan were in Augusta County, Virginia at the same time.  And it's certainly the case that there were interactions between the families -- witnessing each other's legal documents and that sort of thing.  And Cornelius had a grandson named Morgan Bryan (all of Cornelius's sons seem to have adopted the "Bryan" spelling rather than the "O'Bryan" spelling).  So it would also be very valuable to compare the DNA of descendants of Brien O'Brien Jr. and Cornelius O'Bryan with DNA from the descendants of Morgan Bryan.

Bryan DNA resources may be found at:

Genealogical DNA testing is based on testing the Y chromosome.  The Y chromosome is passed down only through an unbroken male line, so direct male line descendants are needed.  Below are my Family Tree DNA results for their 37 marker Y DNA test.  The test strongly suggests Irish origins (which is what I would expect).  The test doesn't mean much else until there is additional Bryan DNA against which to test.

Locus      DYS#       Alleles

1            393         13
2            390         24
3            19*         14
4            391         10
5            385a        11
6            385b        15
7            426         12
8            388         12
9            439         11
10           389-1       13
11           392         13
12           389-2       29
13           458         17
14           459a         9
15           459b        10
16           455         11
17           454         11
18           447         24
19           437         15
20           448         19
21           449         29
22           464a**      15
23           464b**      15
24           464c**      17
25           464d**      17
26           460         11
27           GATA H4     11
28           YCA II a    19
29           YCA II b    23
30           456         15
31           607         14
32           576         18
33           570         17
34           CDY a       37
35           CDY b       40
36           442         14
37           438         12

*Also known as DYS 394

**On 5/19/2003, these values
were adjusted down by 1 point
because of a change in
Lab nomenclature.

A molecule of DNA is a long string of nucleotides that are linked together.  I'm not sure if the proper terminology for a nucleotide is that it is a molecule or not.  But in any case, after the nucleotides are linked together, the string of DNA as a whole is a gigantic molecule.

There are four nucleotides: adenine, thymine, guanine, and cytosine.  They are usually just abbreviated as A, T, G, and C.  These four letters serve as an alphabet for the genetic code.  So a string of DNA may be thought of as a string of letters in the genetic code.  Such a string might look something like GATACCATGCGTA... etc.

Most of the DNA molecules possessed by each person consist of a combination of the DNA from all their ancestors, and the DNA from their ancestors is all mixed together.  The "all mixed together" description is an oversimplification, but it will do for the purposes of this narrative.

The only DNA that is not from all your ancestors and that is not "all mixed together" is Y-DNA, which is passed down only from men to their sons.  And Y-DNA is typically passed down completely unchanged.  So if you are a male, your Y-DNA is identical to your father's Y-DNA that is identical to his father's Y-DNA etc. for generation after generation after generation.  The only exception is that occasionally there is a minor mutation in the Y-DNA.  Were it not for the occasional mutation, every male on earth would have identical Y-DNA.

Actually, I'm obliged to point out that there is a second kind of DNA that is not all mixed together, but rather is passed down unchanged from generation to generation except for the occasional and very rare mutation.  The second kind of DNA that is passed down unchanged is mitochondrial DNA.  It is passed down unchanged from mother to child.  So in principle, mitochondrial DNA testing can be used to trace maternal lines -- your mother, your mother's mother, your mother's mother's mother, etc.  However, the mutation rate for mitochondrial DNA is much slower than the mutation rate for Y-DNA, so that mitochondrial DNA is of extremely limited use for the purposes of genealogy.  What mitochonrdial DNA can be used for is studies of human evolution and migrations over tens of thousands of years.

As compared to geologic time of millions or billions of years, mutation rates in Y-DNA are very fast.  So mutation rates in Y-DNA are very fast as compared to the mutation rates that drive evolution.  However, mutation rates in Y-DNA are very slow by every day standards.  A mutation might occur at a particular place in a string of Y-DNA about once every 500 generations for example.  Fortunately, there are enough different places on a string of Y-DNA where we might look for mutations that the mutation rate is fast enough to be useful for genealogy.

The places on the string of Y-DNA where we look for mutations that might be useful for genealogy are called markers.  A marker contains a short sequence of DNA such as GATA, and that sequence is repeated a number of times. If GATA were repeated three times, we would have GATAGATAGATA.  The short sequences such as GATA that are repeated are called alleles.  A mutation that is useful for genealogy consists of a change in the number of repetitions for the allele.

The various Y-DNA markers have names that have been standardized, such as DYS393.  So in the case of my own Y-DNA, the location known as DYS393 contains 13 repetitions of some allele.  I don't know what the allele consists of (it's probably not GATA), and I don't need to know.  All I need to know is that I have 13 repetitions of the allele at DYS393, my father had 13 repetitions of the allele at DYS393, his father had 13 repetitions of the allele at DYS393, etc. If you went back enough generations (500 on the average), you would eventually find a male line ancestor who had 12 or 14 repetitions of the allele at DYS393 instead of the 13 repetitions that I have.

But one mutation per 500 generations is just an average.  It could have been my father or my father's father, etc. who had the 12 or 14 repetitions of the allele at DYS393.  Because 500 generations is a lot of generations, we look at many more locations than just DYS393.  My own Y-DNA has been tested at 37 locations.  Generally speaking, the more markers in the test, the more discriminating it is in determining if two men are related or not.  Also, some of the markers have mutation rates that are faster than an average of about once per 500 generations.

If two men are related, Y-DNA testing can not determine with certainty how far in the past their common ancestor might have been.  Testing can only provide a statistical estimate.  But again, the more markers there are that are tested, the more accurate the statistical estimate can be expected to be.  Also, as more research is done, more accurate estimates for the average mutation rates of various markers can be calculated, and markers with faster average mutation rates can be found and used.


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This page last edited on 01 Oct 2006.