Using DNA as a Tool for Family Research

Mayo Genealogy Group

6 p.m. Friday 12 May 2023

Park Hotel, Kiltimagh

by Paddy Waldron

WWW version:

http://pwaldron.info/Mayo2023/

YouTube version:

TBA

Introduction

This is a follow-up to my presentations to the Mayo Genealogy Group on 13 May 2017 and on 8 September 2018.
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.

General principles

For every autosomal DNA match, and for every autosomal DNA segment, one would like to assign both to an ancestor. Specifically:

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 crossovers); and
labels become unwieldy if they include full identifying information for husband and wife..

For example:

you share two grandparents with your paternal first cousins; but
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); and/or
triangulated matches (on all the main DNA comparison websites except ancestry.com).

Ahnentafel numbering

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 are female.
The number of any person's father is double the person's number, and a person's mother is double the person's number plus one.
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 1101

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 notation.

Methodology

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

FTDNA Family Finder
- Before 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.

Counter-examples

Matches who end up with multiple dots (e.g. four GGgrandparents):

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.

There is an exception to every rule: not only shared but even triangulated matches can sometimes arise 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 Mar 1840
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 the right.

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 others.
There would be some regions in which:

the two Parkers had an identical segment from a Parker grandparent,
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.

However, these close triangular marriage patterns are very rare.

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:

WikiTree:

Paddy Waldron has four known relatives on WikiTree and in the DNA system
Seamus Bermingham has none (yet)
we are not connected or related (yet)

AncestryDNA:

finds one shared segment (21 centiMorgans) on an unspecified chromosome
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

MyHeritage

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

23andMe

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 that:

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 DNA-based.

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 researchers.
We need to persuade more Mayo people to submit DNA samples to the databases for purely genealogical purposes.
Your 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.