Discussion of DNA research practice

Ian Carswell

Return to homepage


The use of oral and documentary sources for the investigation of family history has always been the traditional tools used in genealogy. Since the 1950’s, scientific investigation of DNA has led to processes which can enable genealogists to precisely categorize specific lines of human and animal descent over considerable periods of time.

As the cost of this testing has decreased, the quality and scientific knowledge has increased to the point that there has been over the last few years a groundswell of enthusiasm to use these tools in the search for knowledge of families origins.

Like many promises of the extraordinary however, the results can sometimes be disappointing if the tools are used incorrectly, the methods badly designed, the expectations unrealistic or the perseveration inadequate.

Some outrageous claims have been made as to the results that can be obtained using DNA analysis. Sometimes they can, but for the majority of us it is just another tool to discover clues which may or may not unravel another tangle in the web of life.    

The fact is, that the families who benefit most from this research are the ones who have already done a lot of work in the traditional areas, and/or who have access to contemporaneous records in which their major lines are known to some extent and the longterm history of the family is also known. This is because the information that is obtained is generally only useful in comparison to another.   Also, the time lines can be significantly longer than people’s knowledge of their family history.

Thus, the families who benefit most are the ones who have good documentation, know the history (esp. of movements and years), can trace back many generations and who are also able to test (and counter-test) all their lines.

The greatest drivers of genealogical research using DNA have undoubtedly been the Irish, and this promises to be of great help for our family study. With historical records dating back sometimes thousands of years, the Irish clan or ‘ tuatha’ have mostly been named along patriarchal lines and have an abiding interest in genealogy. Combined with their preparedness to pay for testing, the Irish families have been at the forefront of this research since the theoretical basis was established within this last decade.

This research has helped to verify that the oral and written histories of the Irish are largely accurate, helped to discover where the peoples of Europe came from and went to, and also helped to re-write early British history which has been shown to be quite misguided in many instances (“history is written by the victors”).

There are currently two modes of DNA testing. The first, (known as Y-DNA), tests specific parts of “Junk” DNA from the Y chromosome of a male.

The Y-chromosome, in the nuclear DNA of every living male, is virtually identical to that of his father, his paternal grandfather, etc., and is carried by male cousins of any degree of relationship that share the same male ancestor. It provides a clear set of “YSTR” genetic marker results expressed as a set of numbers, known as a haplotype, which distinguishes one male-to-male lineage from another.

The Y-DNA results can show:

1.   Whether two or more specific individual men share a common male ancestor and whether that ancestor lived in a time frame of genealogical interest.

2.   If a set of two or more men with the same or similar sounding or meaning surname are directly related through a common male ancestor.

3.   How many different common male ancestors any given group shares.

4.   Unrelated same name clans - so you do not waste time trying to find a connection to same named lines you are not related to.

4.   To which broad pre-history, deep ancestry haplogroup each individual male’s Y chromosome haplotype belongs.

5.     An analysis of the mutations in very similarY-chromosomes can be used to estimate the number of generations since separation from a common ancestor.

Thus, it is possible to tell whether families from different ends of the country (or world) are related, and if so, how close this relationship is. It is possible to mathematically predict (and the tools are available) the approximate time when the separation occurred.

The second method of testing is that of the Mitochondrial DNA (known as mtDNA). The mtDNA test looks at the DNA of the mitochondria, a part of the nucleus of a cell, which is passed on, female-to-child, and inherited down the female line. It is generally used to study long-term population developments such as human migrations. It is a favorite genetic tool of Anthropologists. 

The Mitochondria DNA (mtDNA) test can reveal detail about the distant origins and deep ancestry of your direct line maternal ancestors and could be used to link individuals via the female line. The mtDNA test will also determine your maternal Haplogroup and the area of the world where that direct female ancestor is thought to have lived. 

The mtDNA is not, however, as precise in resolution of time to Most Recent Common Ancestor as the male Y-DNA test, and since the female line birth/maiden names quickly get lost in history, the mtDNA test is thus generally not as useful for genealogical purposes as the Y-DNA test.  But it can be used to confirm scientifically that two people share a common female direct maternal line ancestor if one is suspected via traditional genealogical research.  MtDNA has been extensively studied for over 20 years and is used quite extensively for anthropological studies. Interesting migration maps have been created to show the spread of different female lines throughout the world.

Although large family name groups sometimes contain diverse haplogroups (dictated by historical events such as when and where surnames were actually adopted), there is sometimes also an unexplained anomaly in the data results which indicate a break in transmission of the Y-DNA.

There are five main scenarios to explain a break in the male to male transmission of a DNA signature within a particular family tree traced back from modern times:

There are also at least three additional reasons how males can as it were 'migrate' to another surname which their descendents will keep, in effect starting new more modern genetic lines in that surname:

If you’ve managed to read to the end of this article, then thank you. I hope you enjoyed it. There is so much more to learn, and we are at the very beginning of the DNA story.. Join us in our journey of discovery. Every person and contribution is unique and will shed a powerful torch light on those dim recesses of history.

Return to homepage