Big Y Chromosome Tests
by: John Allred
The Big Y chromosome test is Family Tree DNA’s marketing term for SNP testing.
At the risk of giving too much information I would like to first provide some basic ideas
which hopefully will put us all on the same page.
The letters SNP stand for Single Nucleotide Polymorphism which is an eight-bit term
meaning a mutation by way of a single nucleotide base substitution. Let me explain.
The genetic alphabet consists of four letters representing each of four different chemicals.
These chemicals are called nucleotide bases and their sequence in the large DNA molecule
IS the genetic message (just as sequence of alphabet letters are used to form words).
The initials of the four bases are A, G, T and C. These bases are lined up on one DNA strand, such as
- A A G T C G A C A G T G-
If during copying of the DNA, one base is erroneously substituted for another, such as
- A A G T C A A C A G T G-
this is an SNP or single base substitution, also called a mutation. These kind of mistakes happen
rarely and are observed even more rarely because there are repair enzymes that can recognize
the mistake, take out the erroneous A and reinsert the correct G. The repair enzyme system
corrects almost all, but not quite all, of the mistakes and any that are left can be observed. But the
mutation described affects future generations only if the error occurs during the production of DNA
that will be put into the egg or sperm during the reproduction process. (Most DNA copying occurs
outside the process of reproduction. That is, we all originate as one cell and the average adult has
15 to 50 trillion cells. DNA had to be copied for every one of those trillions of daughter cells and
are subject to the same error/repair system as the reproductive one. But that is another story!)
Now briefly, how does the study of SNPs give us clues about out genetic history? The idea is that if a
group of people stay together for a long period of time, there will be mutations (SNP) happen which is
unique to that group and over time will be spread among that group. This is roughly the definition of a
Haplogroup. Remember the Allred Haplogroup is R1b1a2 and we know that because of SNP analysis
and a lot work to discern where and when that SNP occurred. For example, the SNP that led to the
designation of our “migratory group” as the Haplogroup R1b occurred in Anatolia (includes present day
Turkey, Syria, Iran and Iraq, Georgia) about 10,000 years ago. It is thought that members of this
migratory group spread across Europe over the next several thousand years bringing Agriculture with them.
Now, about 80% of the population of western Europe is from this Haplogroup. The origin, distribution and
migratory pattern has been and continues to be the subject of intense scientific enquiry over the past twenty
to thirty years.
What Big Y proposes to do is to find SNPs on the Y-chromosome of anyone willing to pay $500 and
from those data, they will predict, inform, guess, propose (choose your verb) when and where each of
these SNP mutations occurred and thereby provide a migratory history of the ancestors of that individual.
If this sounds overly ambitious, I think you got it!
Here is what Family Tree DNA says about the Big Y test:
The Big Y product is a Y-chromosome direct paternal lineage test. We have
designed it to explore deep ancestral links on our common paternal tree.
Big Y tests thousands of known branch markers as well as millions of places
where there may be new branch markers. This product is intended for expert
users with an interest in advancing science.
It may also be of great interest to genealogy researchers of a specific lineage.
However, it is not a test for matching you to one or more men with the
same surname in the way that our Y-DNA37 and other tests do.
They have a lot of other stuff on their website that can be categorized as “marketing” but
this seems to be the most clear description of what it is and what it is not. In looking at the results
of the few Allred men who have had this test, the results are shown as the location of a large
number of SNP sites within their Y-chromosome but I see no guidance as what they mean.
Note also that once one Allred male has the Big Y test, all of the Allreds whose Y-chromosome
DNA matches that person would have the exact same list of SNPs. (There may be a difference
of 1 or 2 SNPs but not likely because this kind of mutations happens over thousands, not hundreds,
of years.) And that is my take on Big Y!