Background and Goals


Many genealogists find DNA tests useful. The test itself is simply a saliva sample obtained by scraping the inside of the cheek. The privacy of each tester is protected by analyses being limited to “ancestral markers” rather than to the full personal DNA “fingerprint”. Testers’ names are not disclosed without their consent, and their e-mail addresses are not released to non-testers. See also Privacy Statement. If you as a prospective or existing member of our Study have concerns about privacy/confidentiality issues please e-mail the Study Administrator.

The interpretation of DNA test results depends on the transmission of DNA remaining unchanged from generation to generation, apart from small and occasional changes (“mutations”) in one or more of the “markers” that make up the genetic elements of the DNA profile or signature of each tester. The DNA signatures of individual testers can be compared to establish the likelihood of common ancestry, although DNA test results are never 100% conclusive. Confidence in the interpretation of test results increases as more individuals participate and as the testing and analysis techniques continue to improve.

Four types of DNA test are popular with genealogists:

  1. yDNA Surname Studies. These exploit the characteristic of both y-chromosomes and surnames to only descend by the male line. yDNA tests can be undertaken for three reasons:

    • (a) focussed testing, generally by two testers, to support or refute some specific hypothesised genealogical relationship - effectively a paternity test that is not legally binding;

    • (b) blind testing (aka "fishing"), to seek and investigate genetic relationships ("matches") when compared with other testers in a data base, typically sharing a common surname, for example to explore branches of a surname, break a genealogical "brick wall", or find previously unknown cousins; or

    • (c) deep ancestry studies, i.e. to explore ethnicity issues going back several millennia. For an excellent summary of interpreting ethnicity data given in DNA test results see ; though now dated, the principles remian unchanged. Although htis presentation is discussing ethnicity %s from autosomal tests, the principles are the same for ethnicity %s from y-DNA tests.

However yDNA tests have three important limitations:

- females cannot take a yDNA test, though they are very welcome to participate through a related male tester;

- DNA tests can show a change of surname in the ancestral male line; and

- surnames only go back a millennium, at most.

2. Mitochondrial (mT) DNA tests. These only follow the female ancestral line, and are usually undertaken to support or refute some hypothesised relationship, or for deep ancestry studies.

3. Autosomal (aT) DNA studies such as FTDNA’s “Family Finder” test. These are used to "find cousins", male and female, and test hypothesised relationships, up to 4th or 5th cousins.

4. X DNA tests are similar to aT tests.

This Study only addresses application 1(b) above (see also Ordering Additional Tests). In other words, the Study is not concerned with relationships through female lines identified by mitochondrial or autosomal tests, or with Deep ancestry studies of ethnicity isssues. However individual testers may of course pursue such studies privately, and the Irvine Clan Autosomal DNA Project has been established to develop the potential of Family Finder tests (see A summary of these findings relevant to members of this Study is now included in the Study's main results table.

The relationship of conventional genealogy and surname studies with genetic genealogy (the use of autosomal, mitochondrial and yDNA tests for genealogical purposes) is often confused.

  • Conventional, traditional genealogy, aka "paper trail" genealogy, involves the use of documented sources to trace genealogical relationships of an individual's ancestors and cousins, regardless of surname or gender. Whenever tracing one's own ancestry it is essential to work backwards in time, from the present to the past, from the bottom up. To select a noteworthy historical individual and try to trace his descendants using documentary sources in the hope they include you, i.e. from the top down, is likely to end in failure and disappointment.

  • Autosomal DNA testing can assist traditional genealogical research by identifying possible cousins, male or female, regardless of surname, back for about 5 generations. Like traditional genealogy, autosomal DNA research is "from the bottom up". Autosomal tests, such as FamilyTreeDNA's FamilyFinder test are today the cheapest and most popular DNA test with genealogists.

  • Surname Studies research genealogical relationships within a specific surname. Such studies will typically use both traditional genealogy and yDNA test results. For rare surnames the objective is to collect all the records relating to members or the surname and trace their ancestries. For more common surnames, such as Irwin, this goal is impractical, but even without such diligence there is much to learn from studying a particular surname and its various branches. See for example my book on The Irwin Surname (see Further Reading).

  • A Surname DNA Study such as this uses yDNA test results (primarily) to identify different branches of a surname (aka gentic family) whose members are all related to one another during the surname era, i.e. the past millennium or so, but who are not related to members of other branches of the surname. Such studies are especially useful when conventional research into an ancestral patriline meets a "brick wall", for the relationships identified by yDNA tests are effectively "top down". Typically, for example, a yDNA test result can tell a male American Irwin (or similarly spelled surname) which Scottish or Irish branch of the surname his paternal ancestors descended from, even though his conventional genealogical research does not take his ancestry back to when his ancestors "crossed the pond".

Since 2000 many Scottish Clans have launched surname DNA projects and associated websites. Such projects offer opportunities to:

  • enable direct comparison with other ,members using similar surnames to establish genetic relationships;

  • help conventional genealogical research that has met a “brick wall”;

  • ascertain the probability of two or more testers being genealogically related;

  • identify branches within a Clan;

  • explore, develop and promulgate new ideas.

Turning to the Clan Irwin itself, the genealogical context of this surname Study is discussed at GENEALOGICAL BACKGROUND and in the book The Irwin Surname: its Origins, Diaspora and Early Branches, details of which may be found at FURTHER READING.

Today over 100,000 adult males use the surname Irwin (or one of several spelling variants) throughout the British Isles, in Australasia, and, predominantly, in North America. While many such individuals possess lengthy genealogical pedigrees, very few of these pedigrees have reliably connected the diaspora of the surname. On the other hand some 90% of the testers in this DNA Study have been able to connect their paternal pedigree with a branch of the surname identifiable by its geographic origins.

Goals of the Clan Irwin Surname DNA Study

  1. To facilitate and co-ordinate the STR and SNP yDNA test results of all men bearing the surname Irwin (or variant spellings thereof, including Arvin, Ervin, Erwin, Irvin, Irvine, Irving and Urwin), and of other men sharing similar DNA signatures.

  2. To assess the results of these tests in the context of the traditional division of the surname into Bonshaw, Drum and Orkney branches, and the many other branches that have been identified since the Study was founded, and refine the limits of these branches.

  3. To combine these DNA test results with available genealogical data, particularly to combine the Border Irwin DNA sub-groups now being identified by the L555 haplotree with the pedigrees of members of these sub-groups.

  4. To cooperate with the Irvine Clan Autosomal DNA Project to develop the potential of Family Finder tests involving the name Irwin or its variant spellings.

  5. To promote, co-ordinate and publish analysis and discussion of the results, primarily through the Study’s website, but also through other media such as the Clan Irwin Association's quarterly journal, the Holly Leaf Chronicle.

  6. To facilitate contributions to the wider research, development and understanding of genetic genealogy.

This website does not attempt to describe in detail the underlying principles and terminology of DNA tests for genealogists. For further guidance the following websites all give good background:

FTDNA support a web-based seminar program at:

For a good bit of up-to-date, background reading on the application of genetic genealogy to surnames see:

For those interested in deep ancestry there is a good review at

For an excellent introduction to Next Generation Sequence testing, including BigY, see

See also Further Reading and Supplementary Papers 9 - Lecture Slides