The field of Y chromosome analysis in genealogy is still in its infancy. Techniques and knowledge are rapidly evolving and it is still by no means an exact science. Interpretation of the results is not precise and only provides indications of the probability of family connections at an approximate time or a certain number of generations in the past.

25 Marker Test Minimum Requirement

In order to establish the quality of the interpretation of the Creer DNA Study results, it has been decided that a minimum standard of 25 marker tests should be used.There is a lower resolution tests  available, but is it judged that this would provide an unacceptable number of ambiguous results, which would have to be upgraded to the 25 marker level at additional cost in any case, to resolve any ambiguity. Thus, in order to avoid this situation, a minimum test standard of 25 markers is required.  Details of the costs involved are given here.

How Results are Used

The result will be a string of 25 numbers - representing the genetic signature or haplotype of the individual. FTDNA will automatically search within its existing database of 30,000 chromosome records and identify how many other individuals match exactly. These matches in themselves are not especially significant and indicate only that there may well have a been a common ancestor, but a very long and unquantifiable time in the past. They do however give some indication of deep genetic geographical origins.

Where there is a match with someone with the same surname and similar geographical origin, then this is significant and further examination is then required. As the Creer DNA Study becomes populated, hopefully such matches will be seen within the study participants. FTDNA provide on their website a programme which can be used to calculate the probability of two people having a common ancestor where there are exact or close matches on their 25 marker values. This calculation is a useful tool for evaluating possible family connections, but it not foolproof. When it is backed up with sound genealogical research which supports a connection then it becomes really powerful and meaningful.

The key factors in comparing and interpreting DNA test results are

The degree of fit in marker values - eg 25/25 or 37/37 fit within the same surname indicates a common ancestor. 
The difference in marker values if there is not a complete fit. If there is a 24/25 marker fit and the one marker that is different, is so by a value of 1, then there most likely is a common ancestor - but further back in time. If the difference is by a value of 3 then the probability is that there is no common ancestor.

The rates at which different Y chromosome markers may change over time, or mutate, are still not yet clearly understood or defined. The predicted mutation rate for a Y chromosome marker is used in the calculation to identify the most recent common ancestor (MRCA), by giving some idea of when in the past (number of years or generations) that the particular Y chromosome mutated. 

At the moment however this mutation rate figure is only a empiric average, being about 1 mutation in every 500 genetic exchanges (father to son). It is becoming clearer that different markers mutate at different rates and also perhaps at different rates in different families. As the database of chromosome analyses grows and is compared with known genealogy research, then it is expected that the testing companies will develop more accurate calculations of MRCAs using more refined mutation rates.

Other factors relating to the interpretation of non-matching results due to  "non-paternity" events are described here.

The study coordinator will be responsible for aggregating and summarising the results and analysis as they accrue, as well as guiding participants in the interpretation of their own results.

Additional haplotype matching can be done online with a number of other Y chromosome databases and this can be helpful also


FTDNA also, from their database, are able to make a prediction of each individual's haplogroup - the deep ancestral family group from more than 10,000 years ago. Based on the haplogroups of the people with whom each individual is matched and who have had their haplogroups confirmed with additional testing - then FTDNA makes a prediction about what haplogroup the individual belongs to. This can be confirmed with additional testing, although in most cases the haplogroup is clear enough based on the matches that the confirmation is not necessary, except for the sake of it being confirmed. More information is available here.

Copyright  John A Creer -  Webpage last updated on 12/04/2006