Understanding Y-DNA Testing
for Genealogy Purposes
by Alan Freeman

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 Africa, dubbed the DNA Adam.  This may not have been the biblical Adam because man may certainly have existed before then.  However only this man's DNA line survived to present today.  A religious explanation similar to the biblical story of Noah where only a few men from the same family survived could account for such a happening, however geneticists have not suggested that this is what really happened.  

*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.  

All this boils down to "how can this help me get past my brick wall?"  This is best explained by using my own case:  I can track my Freeman's to 1770 Wilkes County, GA.  There were a number of Freeman's in that area.  Since my ancestor did not own land, we assumed he lived with cousins or parents on  their land.  We assumed some of these other Freeman's HAD to be kin.   

So, we spent years researching all these Freeman's without ever finding a clue that could link us.  I joined the FREEMAN DNA project.  Nearly all the lines from that area of Georgia have tested and I was not kin to any of them!   

Family story has it that our Freeman's came form England into New England then to GA.  My hope is to eventually find a match with a British FREEMAN line which would then put me on course on the other side of the creek.  The biggest help however has been the elimination of wasted time trying to tie myself to lines that can't possibly be kin to us; determined by the DNA testing.  

We have had two Freeman matches, but the mutations show they were 14 generations back and these people can't trace back more than 6 generations either.  Because of the mutations on the 25-marker test, these people would have been kin to me about the time surnames began.  Distant cousins but with no way to tie our families together.  

DNA testing also helped us confirm that our ethnicity is mostly English/British, supporting the family story.  We are also good portions of Irish, Scottish, German, France, Swede and Swiss.  My haplogroup is R1b, which means that it is the most common haplogroup in European populations.  Believed to have expanded throughout Europe as humans re-colonized after the last glacial maximum 10-12 thousand years ago.  It is the haplogroup that contains the Atlantic modal haplogroup (AKA the west coast Europe).

2006 Alan Cole Freeman
This page last updated 01/15/2006