Using DNA as a Tool for Family Research
6 p.m. Friday 12 May 2023
Park Hotel, Kiltimagh
by Paddy Waldron
- This is a follow-up to my presentations to the Mayo Genealogy
Group on 13 May 2017 and on
- On 28 February 2019, AncestryDNA announced "color
coding and custom labeling" of DNA matches.
- On 18 November 2021, MyHeritage announced "Labels
for DNA Matches".
- This presentation will show how I use both.
For every autosomal DNA match, and for every autosomal DNA
segment, one would like to assign both to an ancestor.
- a match who is a known relative can be assigned to the
most distant known individual ancestor through whom you know
that you are related to the match;
- a match who is not a known relative can be assigned to
the most distant known individual ancestor through whom you
are likely to be related to the match;
- a segment shared with a close match can initially be assigned
to the close ancestor associated with that close match; but
- the close ancestor must have inherited the shared segment from
his or her father or mother (unless two siblings by a remarkable
coincidence have a crossover from father to mother in exactly
the same location);
- so segments shared with multiple matches can potentially be
assigned to more distant ancestors (e.g. a segment shared with a
third cousin as well as a second cousin can be assigned to a
greatgrandfather as well as to a grandfather).
Some genetic genealogists have simple family trees and find it
more intuitive to assign matches and segments to ancestral couples
(the most recent common ancestral couple shared with the match)
rather than individuals, but:
- this approach ceases to be equivalent if there are half
relationships or double relationships;
- each segment shared with the match is shared with only one of
the most recent common ancestral couple (barring coincidental
- labels become unwieldy if they include full identifying
information for husband and wife..
- you share two grandparents with your paternal first cousins;
- all of the DNA segments that you share with your paternal
first cousins descended to you through your father:
- some from your paternal grandfather; and
- the rest from your paternal grandmother; so
- the segment is inherited from [grandfather OR grandmother],
NOT from [grandfather AND grandmother].
My own family tree has numerous recent complications which force
me to think in terms of individuals rather than couples:
- my paternal grandfather was an identical twin;
- the identical twins married two sisters;
- the sisters' father married twice; and
- his two wives were first cousins.
Matches who are not known relatives can be tentatively assigned
to ancestors (or predicted) based on
- shared matches (on all the main DNA comparison websites);
- triangulated matches (on all the main DNA comparison websites
- The first step in assigning matches and segments to known
ancestors is to document your known ancestors in a pedigree chart
- I recommend using Ahnentafel (German
for ancestor-table) numbering for various reasons:
- to make it clear to others viewing your match lists that
your AncestryDNA Groups and MyHeritage Labels
and DNApainter groups refer to specific ancestors;
- to distinguish between ancestors in different generations
with the same names (e.g. the reputed seven generations of
Thomas Durkans in my family tree);
- to make the Groups/Labels sort in a logical order.
- Definition of Ahnentafel numbers:
- the subject of the ahnentafel is listed as No. 1
- the subject's father as No. 2 and the mother as No. 3
- the paternal grandparents as No. 4 and No. 5 and the
maternal grandparents as No. 6 and No. 7
- and so on, back through the generations.
- Properties of Ahnentafel numbers:
- Apart from No. 1, who can be male or female, all
even-numbered persons are male, and all odd-numbered persons
- The number of any person's father is double the person's
number, and a person's mother is double the person's number
- The direct male line ancestors (from whom Y-DNA is
inherited) are powers of 2 - 2, 4, 8, 16, 32 ...
- The direct female line ancestors (from whom mitochondrial
DNA is inherited) are one less than the powers of 2 - 3(=4-1),
7=(8-1), 15, 31, 63 ...
- Equivalently, one can use FM notation, following MyHeritage or Double Match
Triangulator (see example):
- the subject's father is F and the mother is M
- the paternal grandparents are FF (father's father) and FM
(father's mother) and the maternal grandparents are MF
(mother's father) and MM (mother's mother)
- and so on, back through the generations.
- If you write the Ahnentafel number in binary notation and drop
the leading 1, then F=0 and M=1
- e.g. mother's father's mother = MFM = decimal 13 = binary
- The FM notation is also useful for quickly identifying
potential sources of X-DNA:
- men inherit X-DNA from their mothers only
- women inherit X-DNA from both parents
- hence X-DNA cannot descend through two consecutive males
- hence an X-ancestor cannot have two consecutive Fs in the FM
I recommend using:
- stars (AncestryDNA, 23andMe, MyHeritage) to distinguish
- matches who are known relatives from
- matches who are not known relatives;
- coloured dots for ancestors:
- MyHeritage provides:
- 30 coloured dots (Labels), exactly enough for:
- 2 parents;
- 4 grandparents;
- 8 greatgrandparents; and
- 16 GGgrandparents.
- filtering by multiple labels selects matches with label A
OR label B
- AncestryDNA provides:
- built-in groups for "Parent 1's side" and "Parent 2's
side" and for "Paternal side" and "Maternal side"
- the user is left to start Relationship assignment and
confirm which parent is which.
- 24 coloured dots (Groups), exactly enough for
- 0 grandparents;
- 8 greatgrandparents; and
- 16 GGgrandparents.
- filtering by multiple groups selects matches in group A
AND group B
- DNApainter provides:
- an unlimited number of colour-coded groups
So I use different methodologies:
- on MyHeritage:
- every known relative has a star and one dot (for the most
distant individual ancestor, back to GGgrandparent, through
whom I am related)
- other matches have a dot for every ancestor with whose
descendant there is a triangulated match
- but I remove more recent dots when I find triangulated
matches with more distant ancestors
- matches attributed to more distant ancestors than a
GGgrandparent have additional notes to compensate for the
limited number of dots
- on AncestryDNA:
- every known relative has a star and one dot for each
GGgrandparent shared or through whom I am related:
- fourth cousins (and more distant) have one dot
- third cousins (etc.) have two dots
- second cousins (etc.) have four dots
- first cousins (etc.) have eight dots
- siblings (etc.) have sixteen dots
- other matches
- are in the groups for "Paternal side" and "Maternal side"
if I cannot attribute shared matches to an ancestor
beyond my parents
- just have a note if I cannot attribute shared
matches to an ancestor beyond my grandparents
- have a greatgrandparent dot if they have shared
matches attributed to a greatgrandparent
- have a GGgrandparent dot if they have shared
matches attributed to a GGgrandparent
- have a GGgrandparent dot and a note if they have shared
matches attributed to a more distant ancestor
- but I again remove more recent dots when I find shared
matches with more distant ancestors
DNApainter, one had to be a little devious to
find triangulated matches directly at FTDNA.
- The Linked Matches (previously known as Assigned
Relationship and before that as Linked Relationship) feature was
designed to identify matches who triangulate with known
relatives, assign them to the most distant individual
ancestor through whom they are related to the DNA subject,
and then dump them all together again in paternal and
maternal buckets, even if they have been assigned to an
ancestor more distant than the father or mother.
- You may want to have two Family Finder kits, e.g. a kit
based on swabs sent to FTDNA with a full pedigree chart for
paternal/maternal phasing; and a kit based on an autosomal
transfer from another laboratory with a minimal pedigree
chart for identifying triangulated matches (e.g. my B95575).
- on DNApainter:
- I use a similar philosophy
- A star emoji can be
copied and pasted into the Match Name to mark known relatives.
Matches who end up with multiple dots (e.g. four GGgrandparents):
There is an exception to every rule: not only shared but even
triangulated matches can sometimes arise by coincidence.
- may be quite closely related to you; or
- may be from the same geographical area and related to several
of your ancestors just by coincidence.
Consider these three marriages in the United Church of England and
Ireland (the established church) in Kilkeedy, County Limerick:
- My GGGgrandfather Thomas Parker married my GGGgrandmother Mary
Keas on 14 Sep 1831
- Thomas's brother Francis Parker married Margaret Smith on 3
- Mary's sister Ellen Keas married Joseph Smith on 26 May 1841
- The two Smiths were also siblings.
- I imagine these three couples sitting around a circular dinner
table, each person with a spouse to the left and a sibling to
However, these close triangular marriage patterns are very rare.
- These three couples produced three families, each of which
were first cousins to the other two, but who didn't have a
single common ancestral couple!
- If one took DNA from one member of each of these three
families, two Parkers and a Smith, then each of them as first
cousins would share many half-identical regions with both of the
- There would be some regions in which:
- the two Parkers had an identical segment from a Parker
- one of the Parkers and the Smith would have an identical
segment from a Smith grandparent, and
- the other Parker and the Smith would have an identical
segment from a Keas grandparent.
- In this example, the three cousins will all "match" each other
genetically, but on closer examination it will be found that
there is no common ancestral couple of all three.
You may still find two distant relatives, related to you through
different ancestors, appearing as shared matches, because they are
related to each other through an ancestral couple whom they share
with each other, but whom neither shares with you.
An example: how am I related to Seamus (James) Bermingham:
- finds one shared segment (21 centiMorgans) on an unspecified
- predicts that the relationship is on my maternal side
(consistent with geography)
- shrinks the shared DNA to 11cM using its Timber algorithm
- reports six shared matches
- including Seamus's fourth cousin
- suggesting that the relationship is through
Seamus's FMFF Michael Carty
- but leaving us to wonder whether or not this shared match
is a triangulated match
- finds one shared segment (21.2cM) on Chromosome 6
- top 10 shared matches and chromosome browser
confirm that his father is almost certainly
related to my mother
- finds two shared half-identical regions (20.31cM on
Chromosome 6 and 5.96cM on Chromosome 9) and an identical
segment of 3.18cM on the X chromosome
- confirms triangulations with two of my known cousins, one on
Chromosome 6 related through my MMFF and the other on
Chromosome 9 related through my MMF
- FamilyTreeDNA shows
that Seamus is related on my maternal side.
- DNApainter confirms
- the segment on Chromosome 6 is shared with another probable
cousin through my MMFF, but this is
- hidden by MyHeritage unless one looks beyond the top 10
shared matches; and
- hidden by FTDNA because all the maternal assignments are
poured back together into the maternal bucket
- and the X-match at 23andMe cannot be through either my
MMFF or his FMFF (two consecutive Fs in each case, and
initial F in his case).
- a 9.0cM part of the segment on Chromosome 6 is shared by
another member of Mayo Genealogy Group
- but she also shares a 7.6cM segment which I have attributed
to my MMMF, so we may be doubly related.
- but care is required because:
- my mother had three grandparents born Durcan/Durkan/Durkin,
allegedly not closely related;
- the evidence for the
sons of my MMFF's parents is largely circumstantial and
Conclusion: Why you should submit your DNA
- The value of DNA "testing" to genealogists
increases dramatically with the number of people from the
relevant geographical area and relevant extended family group
already in the DNA databases used.
- Submitting your DNA to a database has
significant positive externalities for existing and future
- We need to persuade more Mayo people to submit DNA samples to the
databases for purely genealogical purposes.
descendants will be eternally grateful to you for leaving
them your DNA.
- "Fish in all
the gene pools" (AncestryDNA, 23andMe, MyHeritage, FTDNA,
GEDmatch, DNApainter) so that you and your matches can use
all the tools outlined in these presentations.
- See here for all the technical details of how
and why to upload your DNA data and pedigree charts to the