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DNA & Genealogy

Y-DNA: the Direct Paternal Line

All males inherit Y-chromosomes from their father - through his father, his father, his father, etc - represented by the direct paternal line as per the blue boxes on the chart below.


Only males have Y-chromosomes, so only males can take a Y-DNA test.


Y-DNA pedigree chart showing the direct paternal line


If a male has an exact match with another male who has tested, it indicates that they descend from the same male somewhere back in time - but it can't necessarily tell you where and when, as the Y-DNA can remain unchanged for hundreds of years.

Occasional (harmless) mutations can help define particular branches, as once a mutation occurs in a male's Y-DNA, it is passed down subsequent generations on that line.


The pedigree chart below shows (in blue) males who could potentially share the same Y-DNA - providing there are no NPEs (non-paternal events, such as illegitimacies, adoptions etc). 


Pedigree chart showing potential Y-DNA matches on the direct paternal line


A male could potentially share a Y-DNA match with any direct male descendant from any direct male in the pedigree, going back many hundreds of years, not just the generations shown in this chart.


Females can test a male relative (eg. father, brother, uncle, cousin) to determine their paternal ancestry.


Other lines

You are not restricted to testing the Y-DNA of your own paternal line.  If you can find a willing male relative from any other surname/paternal line in your tree (eg. your mother's paternal line), you can test his Y-DNA to investigate that line genetically too. 

In the chart below, for example, you could test a maternal uncle or cousin to determine the Y-DNA of your maternal grandfather's paternal line.  Barring NPEs, you just need a male that shares the surname that you want to test.


Pedigree chart showing a mother's paternal line



Y-DNA testing examines a number of known markers (positions) on the Y-chromosome, and a numerical result is given for each marker. 

Testing is available at different levels - 37, 67 or 111 markers.  The higher level tests will give a more detailed result.

The specific combination of resulting values will determine the Y-DNA haplogroup - which denotes the broad population group those paternal ancestors belonged to.

A standard Y-DNA 37 marker test will produce panels of values, a sample of which is below:


Sample y-DNA 37 marker test results


The sample Y-STR results above are for 37 markers, and predict a common Y-DNA haplogroup of R-M269.

These marker values can be used in surname and geographical projects to compare values between men with the same surnames and men from the same geographical regions.


Surname Projects

Because Y-DNA generally follows the surname line, testers can join a FTDNA surname project to compare origins of other men with the same surname.

Y-DNA generally remains unchanged, but occasional mutations (harmless) can help define particular branches, as any such mutations will continue to be passed down the successive direct male line.


Practical use of Y-DNA testing

Y-DNA testing can be useful for:

  • Connecting paternal lines where no paper/traditional records are available.
  • Determining if males (or families) with the same surname are related.
  • Determining the earliest known origins of a paternal line, by connecting with others who have researched their line further back.
  • Males with unknown fathers (eg. adoptees; donor-conceived) can sometimes determine or get an indication of their biological father's surname through their Y-DNA.
  • Paternity issues:  Do siblings have the same father? 
    Which husband of a female ancestor who married more than once was the father of particular children (eg. surnames of young children may have been changed)?
    In combination with autosomal testing, it can help determine if prevously-unknown cousin matches might be related on the paternal side of the family - or at least help by disproving relationships.


Refer to Family Tree DNA's information page on Y-DNA Basics.

Click the chart below to go to FTDNA's interactive Y-DNA probability chart, which estimates the number of generations to the common ancestor at different testing levels.


FTDNA's Y-DNA generational probability chart


Y-DNA tests are only available from Family Tree DNA.

Also read about mtDNA testing - the direct maternal/female line, and atDNA testing - to find matches on all ancestral lines.




Useful links:



23 Pairs of Chromosomes. One Unique You. Get your DNA story at 23andMe.com.


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  • Mike

    Im just looking for an explanation of the Y-dna probability chart; what the various numbers are?

  • Louise

    Hi Mike,
    If you click on the chart it will take you to a detailed explanation on the relevant page at Family Tree DNA’s Learning Centre. Their chart is interactive, so you can click on the level of testing (Y-DNA111, Y-DNA67, Y-DNA37 or Y-DNA25). Genetic Distance 0 (GD=0) means an exact match to another person at that testing level (all your tested markers are identical, with no differences/mutations), GD=1 means one marker different, GD=2 means two markers different to that match at that testing level. Click on the Y-DNA37 heading. If you have an exact match (GD=0) to another person who has also tested 37 markers, then there is a 50% chance that you share a common direct paternal ancestor within 2 generations (eg. you could be close paternal cousins), a 90% chance that you share a common direct paternal ancestor within 5 generations, and a 95% chance that you share a common ancestor within 7 generations. If you test more markers, say 111 (click on the Y-DNA111 heading), you’ll see that for exact (GD=0) and close matches (GD=1,2,3) at the 111 level, the probability of you sharing a direct paternal ancestor is closer in generations. Effectively this means that the probability of identifying a shared direct paternal ancestor in very recent generations is higher if you have a very close match (eg. GD=0) at the higher level of testing (eg. Y111). If you do a Y-111 test, you may not get close matches at that level, or at any level of testing, but that may just be because the potential paternal cousins have not tested yet, so you can wait and hope for new, closer matches in the future. If you test at the Y-37 level and get exact matches (eg, GD=0), you may consider upgrading to a higher level of testing (say 67 or 111) to see if you still match exactly on the additional tested markers (if the match has also tested to the same level). I recommend you watch this free FTDNA webinar on Y-DNA Markers, Matching & Genealogy.
    Regards, Louise

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