Understanding Y-DNA Testing
for Genealogy Purposes
DNA (Deoxyribonucleic Acid) is a chemical
inside the nucleus of every cell and carries the genetic instructions for
making living organisms. DNA molecules have two stands that wrap around
each other and are joined by rung looking connections between the strands and
resemble a twisted ladder; like in the drawings above and below.
These rung connections between the
strands have particular chemical bases that join them together and
are made of one phosphate molecule, one sugar molecule, and a base. The
bases are adenine (A), cytosine (C), guanine (G), and thymine (T). These
chemical bases and the way in which the molecules join them
create the human DNA code.
Humans have 23 chromosomes. One
member comes their mother and the other from
their father. In 22 pairs the two members are fairly similar.
In females the 23rd chromosome determines the sex of the child and contains the
information for these differences. A female child will have two similar members.
This has been dubbed the X-chromosome. In males the 23rd
chromosome members are dissimilar and are called the Y-chromosome.
One part of the chromosome determines MALE-ness. If the ferilized egg receives an the fathers' X part of the chromosome the child will be
female. If the egg receives the fathers' Y part of the chromosome the child
will be male.
*Side note: Mother Nature takes all
these chromosomes and compares them during the instant of conception and
determines which she thinks are good correct genes and discards the ones
the thinks may be deformed or less favored. Sometimes this may even be random.
These determine ones features and whether one will strongly favor your
mother's lineage or father's lineage.
Male DNA with the Y-chromosome has been
dubbed Y-DNA and comes from the nucleus of the DNA cell. Female DNA comes from
the mitochondria material surrounding the nucleus and has been
dubbed mtDNA.
Most of the Y-chromosome is inherited
without alternation from father to sons, and to their sons, and so on; always
traveling on the male line unaffected by the influence of X-chromosomes that
come from the mother. Each son has his own mothers X-chromosome.
So a father and a son will have matching Y-chromosomes, but each of their
X-chromosomes will be from their respective mothers.
Females inherit two copies of the
X-chromosome, and therefore each gene on the X-chromosome. Males only inherit
one copy (with the exception of a few). A process known as X-inactivation
occurs early embryonic development, thereby causing one copy of a given gene on
either X-chromosome cell to become "deactivated." This
basically is a random happening based on natures
choice.
Because a mothers' legal name change with
each marriage, mtDNA is difficult to use for long-term genealogical research
unless there is a historical trail of the mother's line, such in some Jewish
women.
Certain markers on the Y-chromosome
have been isolated that are unique to generations of man. These markers
relate to parentage and not necessarily to physical attributes and disease
inheritance probabilities.
37 makers or alleles have been
determined useful for genealogical research purposes. These markers
also contain information about your recent ethnic
origins compared against a database of over 146 countries and over 48,306
samples. These markers also compare the Y-chromosome against a database
of 10,268 samples around the world to show from which branch ones Y-DNA
descends. This is know as the Haplogroup and is
associated with man's geographic migration throughout history.
*Currently it has been determined that all
men share Y-DNA markers from a single male ancestor from about 60,000
BC in southern
*To determine full ethnicity from both
parental lines, you must analyze both Y-DNA and mtDNA markers.
There are four main basic types of DNA
testing currently: 12-marker Y-DNA, 25-marker Y-DNA, 37-marker
Y-DNA, and mtDNA. There are other variations, but these are the main ones.
The DNA test is taken by swabbing each
side of the inside of your cheek with a Q-tip stick with a detachable swab the
end that looks like a small toothbrush with a plunger (as shown above).
It is simple and painless and takes a few seconds. The sample swabs are
then sealed in small protective tubes and sent to the DNA lab for
analysis. This takes from six to eight weeks normally, but can take
longer.
The 12-marker test is a beginner test
which can tell you if you are kin to other members with the same surname.
If all 12-markers match another individual with your male surname then there is
a 99.9% probability that you and the other individual share a common ancestor
somewhere in time; Bingo! However if one or more of the
alleles mismatch, then this indicates kin, but that common ancestor was
further back in history. More than a few mismatch markers becomes
un-useful (unless you have a paper trail) since surnames began between 1000-1300 AD, during the Renaissance period.
If you have a 12-marker match then you
would want to compare the other 13 or 25-markers to determine your common
ancestor and likelihood of kin. The fewer mismatches you have, the closer
in time that you and the other individual have a common male ancestor.
The FamilyTreeDNA site www.familytreedna.com has charts to help you determine the near-ness and
probability of your common ancestor with another individual based on the number
and kind of alleles that mismatch. HOWEVER, ideally you are looking for a
perfect or near perfect match.
You may ask, "What do you mean near perfect? I thought that Y-DNA
doesn't change! Well, there are some mutations on the alleles that can
change over long spans of generations. This is called a mutation but does
not mean the person is deformed. Normally the mutation rate is extremely
slow and unlikely, but can happen over a fourteen generation span. Sometimes more often. However a span of this length
basically takes us back to the time when surnames did not exist, therefore it
is useless to concern yourself about that unless you have a paper trail
connecting you to ancestors of that time period. Also some markers have a
high probability of mutation while others are extremely unlikely. This
helps determine the probability and timing.
So having about two or three mutations (or
differences) between another tester of your surname
could indicate that your common ancestor was as far as 1,000 years
ago. This is not very useful if there is no paper trail. However,
sometimes this helps by eliminating other lines with the same
surname; which is one of the main purposes for the DNA project; to narrow
the search.
*It must be noted: There is such a
thing as common DNA. When using a 12-marker test only, you will have
matches on surnames that are not common to your surname. Since there
are only a limited number of alleles tested for genealogical research there are
bound to be repeats of these sequences in other family names. UNLESS
there is a reason to believe that your surname changed or there was some illegitimacy
in the line, then there is no reason to pursue these matches. And you can
setup your access so that you can hide or show this
unlikely matches. It is very difficult and near
useless for a male of unknown lineages to use these comparisons to
find his paternal line.
FTDNA
offers confidentiality, although the DNA used for these tests would be pretty
useless except for paternity cases. You are contacted by email when
others match your DNA profile. You can choose to follow up or ignore
them. It is recommended that you begin with a 25-marker test and have it
upgraded later to the 37-markers only if you actually find 25-marker
matches. Hopefully this will eventually happen! Many participants have
had 12-marker tests only to find that several of the remaining markers mismatch
and as we said, this can quickly add up to several hundred years
difference.
Incidentally, the National Geographic
Society and IBM has a volunteer Genographic Project in which they are attempting map how humankind
populated the earth. If you chose to opt-in, your DNA
could help map the migration of man.