Using DNA for Family History – British Isles by County

The primary aim of the British Isles by County project is to achieve a spatial visualization of the distribution of Y-DNA haplogroups and mtDNA haplogroups in the British Isles. A clearer picture of the distribution of Y-DNA and mtDNA haplogroups across the British Isles will aid in understanding the migration and settlement history of this region of the world. For a detailed discussion of the genetic history and makeup of the British Isles see the Wikipedia article here.

The project will also be of assistance to genealogists by helping determine where a particular surname, and more particularly, haplogroup is concentrated within the British Isles. Consequently, members are encouraged to take those tests which will refine their haplogroup assignments. For Y-DNA, this means all available Deep Clade, or SNP tests. For mtDNA, this means the Full Sequence.

Family Tree DNA has produced a series of Webinars to cover the basics of its DNA tests and the interpretation of results, essentially everything included in the FAQ topics. Before you go any further, we suggest that you view the Introduction to Family Tree DNA and myFTDNA: Managing your Personal Account videos. The full suite of webinars can be accessed on the FTDNA Youtube channel here. Debbie Kennet's Beginners Guide to Genetic Genealogy offers a very balanced and up-to-date video introduction to subject of DNA testing.

For detailed answers to your questions, you may wish to consult the Family Tree DNA FAQ. The Y-DNA section, the mtDNA section, and the Family Finder section of the FAQ cover the material you will find below and more.

It is also recommended that you frequent the myFTDNA User Guide to learn how to manage your tests and derive the greatest benefit from your experience with genetic genealogy. The FTDNA Expert's Guide provides a more detailed treatment of the topics covered in the above pages.  

N.B. It is vitally important that all members enter information on their Most Distant Ancestors (known) in the Direct Paternal line and the Direct Maternal line, as well as the corresponding Ancestral Locations. This is done from your MyFTDNA page using the Most Distant Ancestors Selection from the My Account menu (in the dark blue bar running across the page). Should you require assistance with this procedure, please contact one of the Administrators. 


Getting Started with Genetic Genealogy – Understanding your Results

Logging in to the Family Tree DNA website

Understanding Y-DNA STR Markers

STRs, or Markers

The 76 Trombone Method

Using Surname Distribution Maps to Research Near Matches

The 1841 Census

The Project Results Page Database

Understanding mtDNA

Autosomal DNA – Finding Family

ADSA in Action

The Business End: In Common With (ICW)



Getting Started with Genetic Genealogy – Understanding your Results

Once you have received your test results, you will manage your genetic genealogy research from your myFTDNA page. To access your myFTDNA page, follow these steps:

Logging in to the Family Tree DNA website:

1. In your web browser, go to

2. Click on the SIGN IN button (blue) in the upper right corner.

3. A new page will open. Enter the kit number and password that were assigned to you when you received your DNA test kit in the appropriate boxes on the left of the page. Press the orange LOG IN button.

4. Your myFTDNA page will open, as identified by the logo in the upper left corner. Below the logo is a dark blue menu bar. To the right on the menu bar is a button you can click to Order an Upgrade. Your name and kit number will appear in the upper right corner, where there is a link to Logout.

5. On the left is a box titled Your Account. This contains sections where you can view your Complete Order History, Manage Projects, and Manage Personal Information/Profile, or Change Password.

6. To the right is a section containing prompts for new tests or maintenance operations, such as Family Finder and Add Your Surnames. If you have tested Y-DNA, you will also see your Y-DNA Haplogroup and/or mtDNA Haplogroup expressed in short form, i.e., with the name of the SNP, plus any detailed information about your haplogroup, such as identification as the Western Atlantic Modal Haplotype.

7. Below this are rows of buttons with which you to access information about your DNA tests. The functions accessed through the buttons here are also available from the menu headings at the top left of the myFTDNA page, next to the myFTDNA logo.


Understanding Y-DNA STR Markers

Since we do not have the luxury of time travel, genealogists researching their family histories may supplement paper research with the next best thing: the time-capsules of DNA in all our cells. To glean genealogical information from your Y-DNA test profile, you must look for Y-DNA profiles that are a perfect match or contain only a few markers different from yours. Depending on the number of markers you have tested (12, 25, 37, 67, 111), the persons most closely related to you genetically, in the direct paternal line, are those with the fewest mismatches. If you tested only 12 markers, you may have many perfect matches, but these will not provide you with much, if any, information about your genetic relationships, as this test is too general in scope. If you tested 37 or 67 markers, on the other hand, and you have found perfect matches or near matches, i.e., with up to 4 mismatches on 37 markers or 7 on 67 markers, you may be able to learn a great deal about your ancestral relationships, as well as the history of your direct paternal line. You must always bear in mind that Y-DNA traces only the direct paternal line, and thus normally corresponds to the ancestral line of males bearing the surname of the testee.

We will look at the different ways you can learn from your Y-DNA results. Remember, always check for matches (or mismatches, genetic distance) on the highest number of markers tested first.

Note: For each test shown on your MyFTDNA page the date of the last completed test will be displayed next to the test name. An upgrade button will also appear if further tests are available to you for a given type of DNA.

More detailed information can be found in the Y-DNA section of the Family Tree DNA FAQ.

STRs, or Markers

Lists the standard Y-STR values, i.e., the values of the Y-DNA markers tested. These values can be downloaded if you wish to place them in a spreadsheet in order to do comparisons.

Click on this button to see the number of your (near-)matches per country, and as a percentage of the number of testees with ancestry in that country. The results are shown for the number of markers tested, including exact matches and mismatches. The higher the Percentage for a country or region, i.e., the Match Total divided by the Country Total, the greater the likelihood your ancestor lived in that country or region. Look at the percentages for the highest number of markers tested first.

View maps showing locations of matches and near matches for different numbers of markers tested. There are buttons to Show Match List and Update Ancestor’s Location (strongly advised if you have not entered this information), and another button for Understanding Your Matches.

This is where you will find detailed information about your matches and near matches with other persons who have tested Y-DNA with FamilyTreeDNA. You can Filter Matches down to one project, or show matches to the entire FTDNA database (preferred). You can also set the number of Markers, as well as the Genetic Distance (up to 10 steps on 111 markers tested). For best results, choose the Entire Database, and show maximum Distance for the number of Markers that yields the matches and near matches. For example, if you have a 1 or 2 step mismatch on 67 or 37 markers with another person of the same surname, you are most certainly related to that person, and you may even have been able to document the relationship. Mismatches on as few as 25 markers can provide helpful information about your direct paternal lineage history. Again, the Page Help button will provide you with detailed explanations of the information appearing here. SNPs will be discussed under the Haplogroup button.

At greater than 1- or 2-step mismatches, relationships may be more distant, while at larger numbers of steps you might find mismatches with persons of different surnames. Normally, this is indicative of a deeper ancestry, i.e., a relationship that precedes genealogical time, or the era in which surnames were adopted: for the British Isles, this means roughly 800-900 years ago, or more recently in some regions.

The 76 Trombone Method

Charles Moore recently pointed out in the U106 forum on that limiting the search range with the Filter Matches can often reveal connections that may have been hidden in a forest of matches on lower numbers of markers. Let us say you have too many matches and near matches on 12 markers to process efficiently. From you MyFTDNA page, when you search Y-DNA Matches, use the Filter Matches settings to Show Matches for the British Isles by County project only, on 12 Markers with Distance set to Exact Match. Press Run Report. This will pare down your hits considerably. Sorting by haplogroup will bring all the hits in your subclade together for close inspection. Since you will see only exact matches on 12 markers, you may be able to identify a pattern in the distribution of hits turned up in the results. You can then compare this distribution with what you find in a haplogroup project you might have joined, since the members of your subclade are probably not so distant mismatches on STRs too. If some of these genetic cousins have uploaded pedigrees, you may find it instructive to examine them for possible clues to connections. Repeat the operation with higher numbers of markers if applicable.

Using Surname Distribution Maps to Research Near Matches

By comparing regional distributions of surnames appearing among your mismatches with the distribution of your own surname in the British Isles, you may be able to identify the region in which the earliest bearer of your surname lived. The method is not a panacea, and may sometimes be of little help. The procedure is as follows.

1. Log in to the Great Britain Surname Profiler here and click on the blue Search for a Surname button.

2. Set the year of your search to the 1881 Census.

3. Type your surname in the box, and press the blue Find bar.

4. A map of the British Isles (excluding Ireland and some of the Islands) will appear, together with an inset regional map of Greater London. Concentrations of surnames will be shown with a colour gradient.

(You may take as a rule of thumb that a surname will show the highest density in the area where it originated, though this may not be true in all cases, especially where high densities occur in London and sometimes in the main industrial and port towns; these densities may reflect migrations that occurred during the Industrial Revolution.)

5. Right click on the map and Print it to a printer or PDF file. Be sure to label it with the surname and year.

Repeat the same steps with any surnames showing mismatches to your Y-DNA profile, beginning with names having the fewest mismatches, i.e., those surnames that are probably more closely related to you. Create maps for surnames showing mismatches on 25 or more markers tested. It is advisable to use a higher number of markers tested whenever possible.

6. Once you have produced the maps, examine them to locate regions where surnames overlap, especially high density regions. Because the map boundaries utilized by the Surname Profiler do not correspond to historical county boundaries, you may wish to consult the pre-1974 boundary maps on Genuki here. Genuki also offers a very handy gazetteer with a place finder and handy mapping feature here.

Areas of overlap may indicate where your surname originated and help guide you in your documentary research. Such overlap will normally be of greater relevance to your ancestry the more localized a surname is, i.e., the less widespread its distribution throughout the British Isles.

Note that the 1881 Census data for England and Wales can also be broken down to a smaller administrative unit, the Poor Law Union, or PLU. Should you wish to have a PLU distribution map of any surname, please contact the administrator here. Be aware that some surnames may not have existed in sufficient numbers to be included in the Surname Profiler. Contact the administrator to check whether a solution exists in such cases.

N.B. If your ancestry points to Scotland, it may be possible to identify a probable region of origin for your ancestors using a clan map of Scotland, such as the Highland Clan Map here.

The 1841 Census

The 1841 Census may show an earlier state of a surname’s distribution within England, Scotland and Wales. If you have access to, you can search the 1841 census records for your surname. Be sure to use variants of the surname, as spelling is almost never constant, and use all the regional versions of the census (England, Scotland, Wales, the islands). A potentially more precise strategy is to limit your search to males above a certain age who were born in the county in which they lived at the time of the census. The results of your search should then better reflect the early distribution of the surname before the Industrial Revolution uprooted many families.

Should you wish to receive a distribution map of a surname from the 1841 census, please contact the administrator here.




A button on this page enables you to upload your DNA profile to the Ysearch public database maintained by FTDNA. See below.

Click this button to show the country of origin of matches and mismatches to you, but this time according to haplogroup, i.e., deep ancestry. In general, the more refined the haplogroup designation, the nearer, or less distant, the ancestry.

The branches of the haplotree are defined by SNP mutations, each corresponding to a specific haplogroup. Your Confirmed Haplogroup will be shown in SNP shorthand at the top of the page. Use the Haplogroup FAQ, Nomenclature FAQ, and Define Haplogroup buttons to obtain detailed information about haplogroups and the conventions adopted by FTDNA. Assuming a subclade has been identified for you, it will be identified on the tree in green as the lowest SNP for which you have tested positive. SNPs that have tested negative will be marked in dark red, and available tests are shown in orange.

For the purposes of the British Isles by County project, you are encouraged to take all available SNP tests so that the project mapping can be carried out with the most detailed subclade assignments possible. Note that the Big Y test and subsequent developments have established a new depth of subclades in the Y-DNA tree. Refining your subclade assignment can also be helpful in identifying closer relations among persons showing larger numbers of STR mismatches that can be investigated on the site. You are also encouraged to join the haplogroup project corresponding to your terminal SNP mutation, e.g., R1b-L48. Haplgroup project administrators are especially knowledgeable and will be able to make recommendations for further SNP tests if these are warranted.

The SNP map is a powerful mapping tool that accomplishes some of what the British Isles by County project was created to do. The map tool can be used to plot the geographic distribution of instances of a haplogroup, including one or more of its subclades, in the Family Tree DNA database. Once a haplogroup and subclades have been selected, the reliability of the plot can be refined by reducing the cluster size (in either miles or kilometres). The smaller the cluster size, the more data points will be rejected as unreliable. The two examples below illustrate the result of reducing cluster size. The R-U106 map on the left shows the result for a 100 mile cluster, while that on the right is a plot of a 10 mile cluster. The current theory that R-U106 could have spread into the British Isles from the eastern Rhine valley tends to be confirmed by these plots.

If you would like to see a map for your subclade, please contact me, indicating the exact subclade you wish to have plotted.

The Project Results Page

The colourized Y-DNA results for the British Isles by County project can be found here. The results are organized by County subgroups. If you do not know the county of origin of your direct paternal line, you may be able to identify possibilities by searching within each county for persons of the same haplogroup, preferably a subclade, as yours. A listing of SNP results by haplogroup for the British Isles by County project can be found here. A haplogroup in red is one that has been predicted on the basis of STR markers, while a haplogroup shown in green has been confirmed by SNP (Deep Clade) testing. A confirmed haplogroup will enable you to narrow down relevant matches when you have multiple near matches on STRs. Confirmed haplogroups are also of great benefit to the British Isles by County project in that they make it possible to produce detailed maps of deeper subclades.

Persons who cannot be assigned to a County subgroup are assigned to a Haplogroup subgroup. If you find that you have not been assigned to the correct subgroup (County or Haplogroup), please contact one of the administrators for assistance. Database

Another very valuable resource for genetic genealogy is available at Once you have uploaded your DNA profile to Ysearch from your Matches page, you will be able to search for mismatches at a greater number of steps than the limit on the FTDNA Matches page. (The maximum number of mismatches that will be shown on your Matches page is 10 on 111 markers tested.)

To access Ysearch, click on the  button at the bottom of your Matches page. You will not need to edit your User profile if the information already uploaded from FTDNA is already complete. Simply click on the  tab at the top of the page, and if your user ID is displayed in the box on the Search Genetic Matches page, press the Search button next to it.


Now you are on the Enter Search Parameters page. Note that every search you initiate from this page requires that you enter a human testing (captcha) code. If you neglect to enter the code or make an error, the Search will not be executed.


First, you must select a minimum number of common markers. If you tested 67 STR markers, for example, you might wish to select 66 as the number of markers tested, in case a marker may have had a null value. Under Allow, select maximum genetic distance of 1 per marker compared above 50 markers, as a start, which will yield up to about 25% mismatches on the total markers. There is no need to Limit the search by last name unless you have already identified a large number of near mismatches and wish to narrow your results.

Next, enter the recognition text in the Type the text box. If you have already executed a search and wish to reduce the number of search results further, you can Limit by Haplogroup or Region. Limiting by haplogroup is normally a very helpful refinement, but only after you have done a preliminary search that produced a substantial number of results and you wish to exclude mismatches which do not fall within your haplogroup. (Consequently it is always best to confirm your haplogroup assignment with SNP testing.)

You can also search on fewer markers tested if your search does not yield results initially.

Press the Search button. Experiment by increasing or decreasing the compared above value until you produce, say, double or triple the number of results appearing on your FTDNA page. Be sure that the radio button for compared above is selected before you initiate a search.

Among your search results you may see modals for different subclades, which of course do not all correspond to your haplogroup. Only the modal corresponding to your terminal SNP is relevant to you.

The new surnames that may appear once you have reduced your results to a manageable number can then be used to further refine your search for the region in which your surname originated, as described in the Matches section above. Further information on the use of Ysearch can be found here.

Understanding mtDNA

The utility of mtDNA for genealogy is chiefly in terms of deep ancestry, as mutations occur much less frequently in mitochondrial DNA than in Y-DNA owing to the very small number of chromosomes making up the mitochondrial genome. Unlike Y-DNA, mtDNA does not trace a single surname, since it is transmitted by mothers to their children: every male and female receives mtDNA from the mother only. mtDNA tests cover three regions, Hyper Variable Regions 1 and 2 (HVR1 and 2) and a separate Coding Region. A full mtDNA test includes all three regions. Variations are expressed as SNP differences from the Cambridge Reference Sequence, which is an arbitrarily chosen member of Haplogroup H2a2a. 

More detailed information can be found in the mtDNA section of the Family Tree DNA FAQ.


Most of your matches will be on HVR1. If you tested mtDNA, you can access your results from the following cluster of buttons.


Click this button to see a list of matches, including Names, Most Distant Ancestor, mtDNA Haplogroup and Match Date. You can select the Level at which you wish to see matches displayed (HVR1, HVR1 and HVR2, or HVR1 and HVR2 plus Coding Regions). The levels you can display will depend on the tests you have ordered from FTDNA: mtDNA, mtDNAPlus, mtFullSequence. (Note that basic mtDNA is no longer offered, even though results may be shown for the HVR1 level.) Up to 3 mismatches may be displayed on the full sequence test. However, at any level, given the low rate of mutation of mtDNA, only exact matches are likely to be of genealogical interest, since the most recent common ancestor of any mismatches is likely to be too far removed in time. Still, clues may be provided by the surnames that appear, even among mismatches, as surnames may be preserved in given names or be present in reconstructed pedigrees, even in altered forms.

Advanced Matching

The advanced matching feature enables you to view and combine matches from 3 different types of test: mtDNA, Y-DNA and Family Finder.

Ancestral Origins

Click on this button to view ancestry information for your mtDNA matches, including Country, your total number of matches and the number in the entire database for each country, and the percentage of your matches to the database total. The percentage is not intended to reflect the degree to which your ancestry is traced to a given country. It should be thought of more a relative probability that your ancestry can be traced to that country. In the case of the British Isles, the total number of matches may be higher than matches for other countries, though the percentage may actually be lower. This is due to the large number of testees whose ancestry is traced to the British Isles.

Matches Map

Here you can view the geographical distribution of your matches for each level of testing (HVR1, HVR2, Coding Region).

Migration Maps

Click this button to view maps showing haplogroup migrations and the frequency of major haplogroups by region. Your haplogroup’s proposed point of origin and historical migration will be indicated on the first map.

Haplogroup Origins

Click to view a list of countries of origin for your matches in the FTDNA database, including the number of matches per country.


Upload your DNA profile to the mtSearch public database maintained by FTDNA.


Autosomal DNA – Finding Family

mtDNA and Y-DNA are limited in potential for genealogy purposes by the fact that inheritance is traced only in a direct maternal or direct paternal line. All other contributors to the subject’s genome are excluded from the picture. Autosomal DNA fills this gap, although its effectiveness is restricted in terms of the number of generations that can be reliably traced to a common ancestor: typically 5 or 6. For a quick introduction to the subject see Kimberly Powell’s article here. A brief discussion of triangulation can be found here, while Debbie Kennet's lecture Understanding autosomal DNA testing - the pleasures and the pitfalls provides an account of the latest developments in autosomal testing and interpretation. For a detailed description of the tools available on the Family Tree DNA site for analyzing and interpreting the Family Finder test, see the Family Finder section of the FTDNA FAQ.


Here we will walk through a simple but highly efficient tool mentioned in Ms. Powell’s article: The Autosomal DNA Segment Analyzer, or ADSA for short. Be forewarned: the use of this tool requires that your autosomal DNA data and genetic relationships be transferred to a site external to Family Tree DNA for processing into comprehensive table of results. The advantage of this procedure is that all your matching information is available in a single, readily understandable HTML file. Interested parties should read the text of the Web Site Agreement on the login page here.


Family Finder is at its most powerful if, in addition to the subject, all of grandparents on both the maternal and paternal side have also taken the test. In the absence of grandparents, siblings, cousins and uncles can be substituted with some loss of resolution. The goal is to identify segments of DNA on each chromosome that were inherited from one or another of these grandparents in order to place partial matches you may find in Family Finder in a particular branch of your ancestry. Once you have begun to sort out the lineages in which your FF matches fall, you will be better able to process information you may glean from pedigrees associated with these matches.

Since the Family Finder module of FTDNA is well described in the links above, we will mention here two third-party analytical tools which may be of service to persons who have tested autosomal DNA.

ADSA in Action

With the above caveats in mind, here is how to drill down into your autosomal DNA with the DNAGEDcom tools.

1. Go to the ADSA login page and click on the Register link. Create an account by filling in the boxes.

2. Once you have created your account (and recorded the username, password, and identifying question for future reference), click on the Family Tree DNA tab, and select Download Family Tree DNA Data.

3. Enter your FTDNA kit number and password, and a figure of 5 for the Minimum cM.

4. Click Get Data, and wait patiently until all processes have been completed. A total of 3 files will be downloaded and processed into a Zip file. The file has normally been created when the progress bars fill the boxes, but sometimes it takes a bit longer.

5. Next, under Family Tree DNA, select Download FTDNA GEDCOM, and follow the instructions on the download page.

6. Once you have done this, under Autosomal Tools, select Autosomal DNA Segment Analyzer. Read through the text on the page to familiarize yourself with the procedure. If you wish to explore the methodology further, you can click on the links for detailed instructions and sample output.

7. In the box on the bottom left, enter the Family DNA kit number for which you downloaded Family Finder data in steps 2 to 4.

8. Click the GRAPH button. A new browser window will open containing a very large chart of your autosomal DNA matches by chromosome. This file may take some time to build.

9. Save the file to your computer.

You now have, in a single file, complete information on your Family Finder matches with 5 or more centimorgan segments in common with you, including names, start and end points of matching segments, number of centimorgans and SNPs in a matching segment, an email address with which to contact the match, and a very handy colour coded In Common With (ICW) matrix you can use to triangulate matched segments, which in turn are depicted as coloured bars in the right-hand column. Everything you need is at your mousetip, with extra detail displayed when you hover over a column.


A detailed description of the triangulation methodology you can follow with this file is provided on Don Worth’s How To page. The following is a summary of the methodology.

1. The first third of the How To file is covered in the above steps. Once these steps have been completed, you can work in the ADSA output file.

2. If you hover your cursor over a name in the MATCH NAME column, a box will appear showing the date of matching and a probable relationship, as well as a list of surnames in the person’s pedigree, if the surnames were provided. These can be helpful to you in determining in which branch of your tree the person has a common ancestor with you. You will have to go to the FTDNA Family Finder page to find out whether the person uploaded a GEDCOM file you can view.

3. The next four columns specify the START and END points of a shared segment, as well as the number of centimorgans and SNPs in the segment.

4. The segment size is depicted visually in the SEGMENTS column on the right (though the lengths are not to scale). Hovering over a segment will bring up a box containing Total Shared cMs with this person (all chromosomes), the longest shared block in cMs (on any chromosome), and a list of all the matching segments you have with this person, plus a list of persons who have this segment In Common With you.

5. You can send an email to the person directly from the ADSA file by clicking on the address.


The Business End: In Common With (ICW)

6. In the ICW column are coloured matrices, or sets of “bricks,” which you can use to triangulate a common ancestor. When segments appear as stacked in the SEGMENT column, they form a matrix in the ICW column, representing the fact that portions of the segment are shared by all the persons appearing in the rectangular matrix.

6. Corresponding to each coloured segment in the SEGMENT column, and on the same line, is a “brick” in one of the ICW columns that is of the same colour as the segment. This brick is marked by a diagonal line. Here we will refer to the brick or box containing the diagonal line as the vector.

7. Above and below the vector in the ICW matrix will be a column (sometimes broken) of bricks of the same colour as the vector, and of course also of the same colour as the shared segment shown as a bar in the SEGMENT column.

8. Each segment in the row corresponding to one of the coloured bricks in the ICW vector column is shared with you and with the person in the row, and with all other persons with coloured boxes in the vector column. You all have the segment marked by the vector IN COMMON, and therefore have a shared ancestry.

9. When a series of vectors align diagonally and their coloured bricks form a rectangular box, all the matches corresponding to the rows in the box are ICW each other and probably all share a common ancestry.

10. If you scan up and down the ICW vector column, any match to the vector you may find in another row that shares the same sequence of coloured bricks as appear in each line of the ICW rectangle also shares ancestry with the matches in the rectangle. However, these matches lying outside the rectangle also share DNA with other matches that is not ICW the matches falling within rectangle. These matches may be included in another rectangle that is not ICW with the first rectangle.

11. When segments overlap in the SEGMENT column with segments of members of an ICW rectangle, but the corresponding vector bricks do not form part of that rectangle, or instead form a separate ICW rectangle, these persons match you but not the members of the first ICW rectangle. The members of this ICW rectangle thus inherited the chromosome from the opposite parent to the members of the first ICW rectangle: if the first ICW rectangle represents paternal inheritance, the second represents maternal inheritance, and vice versa.

12. Small rectangles show a greater likelihood of common ancestry, as very large blocks of bricks may represent short shared segments that are not Identical By Descent (IBD, i.e., due to a common ancestor), but Identical By State (IBS, i.e., due to chance). If you set the Minimum cM to 5 when you downloaded your FTDNA Family Finder data, you will rarely find such structures. A safer minimum might be 7 or 10 cM.

13. In analyzing the data contained in the ADSA file, the most productive strategy is to examine long segments first, as these are more likely to be related within the reach of your known family tree. Find ICW rectangles within the range of the long segments, and inspect the names that appear when you hover over the corresponding segments, looking for surnames common to your own ancestry.

14. It is also helpful to look at matches that do not form part of a box to see if the matches also have DNA in common with you on another chromosome. You can then shift your attention to that chromosome, where the match may belong to a vector rectangle with other matches. Once again, inspect the segments for names you know from your own ancestry.

A fuller presentation of the ADSA triangulation methodology is to be found in Don Worth’s How To page. Please donate to the DNAGedcom site if you find it helpful.

If you require assistance in creating your ADSA file from your FTDNA Family Finder data, please feel free to contact me here. for assistance

A personal note: in spite of the fact that autosomal DNA is branded as a near-term genealogy tool, I frequently find surnames that are not represented within my own tree in recent generations. Notwithstanding the possibility of an NPE explanation, these are often names I might expect to be distant genetic cousins. Does Family Finder have an undocumented Turbo mode?


Another third party utility for analysis of autosomal DNA is GEDMatch. An instructional video is available here.