Using Genetic Genealogy to Reconstruct our Family History

All Aboard 2017 initiative / Lifelong Learning Festival

7:00 p.m. Tuesday 4 April 2017

T1.15, Ground Floor, TARA Building, Mary Immaculate College, Limerick

by Paddy Waldron

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What is Genetic Genealogy?

Where does our DNA come from?

male offspring female offspring
sperm Y chromosome X chromosome
22 paternal autosomes
egg X chromosome
22 maternal autosomes

Inheritance paths

Y chromosome
Only males have a Y chromosome.
The Y chromosome comes down the patrilineal line - from father, father's father, father's father's father, etc.
This is the same inheritance path as followed by surnames, grants of arms, peerages, etc.
X chromosome
Males have one X chromosome, females have two.
X DNA may come through any ancestral line that does not contain two consecutive males.
Blaine Bettinger's nice colour-coded blank fan-style pedigree charts show the ancestors from whom men and women can potentially inherit X-DNA.
Exactly 50% of autosomal DNA comes from the father and exactly 50% comes from the mother.
On average 25% comes from each grandparent, on average 12.5% comes from each greatgrandparent, and so on.
Due to recombination (see below), one might inherit, for example, 27% from the paternal grandfather and 23% from the paternal grandmother.
Siblings each inherit 50% of their parents' autosomal DNA, but not the same 50% (except for identical twins).
Similarly, siblings each inherit 50% of their mother's X DNA, but not the same 50% (except for identical twins).
Sisters each inherit 100% of their father's X DNA.
Everyone has mitochondrial DNA.
Mitochondrial DNA comes down the matrilineal line - from mother, mother's mother, mother's mother's mother, etc.
The surname typically changes with every generation in this line.
For genetic genealogy, beginners should start with autosomal DNA, or with Y DNA for one name studies or surname projects.

How much DNA do we have?

Billions of letters:
Male Female
Length Width Total Length Width Total
Autosomal 2,881,033,286 2 5,762,066,572 2,881,033,286 2 5,762,066,572
X 155,270,560 1 155,270,560 155,270,560 2 310,541,120
Y 59,373,566 1 59,373,566 0
Mitochondrial 16,569 1 16,569 16,569 1 16,569
GRAND TOTAL 3,095,693,981 5,976,727,267 3,036,320,415 6,072,624,261

How much DNA do we observe?

The three major DNA companies (see below) sample different locations on the autosomes - about 0.02% of the total:
The overlap between FamilyTreeDNA and the original AncestryDNA set is 652,462 (based on my personal results).

The random component of DNA inheritance

Most DNA is transcribed exactly from the relevant parent.

Two sources of randomness mean that one cannot always exactly infer the child's DNA from the parents' or vice versa:
Mutations are transcription errors at single locations, e.g. a single A in the parent may be replaced by a C in the child.

Some locations mutate very frequently (every couple of generations), and can be used to identify individuals beyond reasonable doubt, e.g. in criminal cases.

Some locations mutate less frequently (only once in many generations or once in the history of mankind), and can be used to identify closely or distantly related individuals.

The vast majority of DNA is identical for all humans, and even for many of the apes.

Special types of mutations:

Y-DNA Mutations

The entry-level Y-DNA37 product looks at the numbers of repeats for each of 37 STR markers on the Y chromosome, e.g. Clancy Surname Project or The Marrinan Family or O'BRIEN Y-Chromosome DNA Surname Project.
Some SNPs on the Y chromosome are once-in-the-history-of-mankind events and can be used to build a Y-DNA Haplogroup Tree.
STRs can predict Y haplogroups but a SNP product must then be purchased to confirm the Y haplogroup.
Surname-specific SNPs are now being discovered.

mtDNA Mutations

There is also an mtDNA Haplogroup Tree.

Autosomal DNA Mutations

The 0.02% or so locations observed on the autosomes are known SNPs.
All observed SNPs are still weighted equally in relationship calculations, but two individuals who share a mutation observed in only 1% of the population are likely to be far more closely related than two individuals who share a mutation observed in 50% of the population.


The other source of randomness is recombination, which is how, e.g., the father's paternal and maternal autosomes cross over to produce the child's paternal autosomes.

The double negative approach: opposite homozygous locations and half-identical regions

False positives can occur - a long half-identical region can by chance consist of short overlapping (or zig-zagging) paternal/paternal, paternal/maternal, maternal/paternal and maternal/maternal segments.

Phasing and triangulation are like opposite sides of the same coin:
Rule of thumb for lengths of the longest half-identical region::
The aggregate length of all the half-identical regions above some arbitrary threshold is used to estimate the relationship:
Average autosomal DNA shared by pairs of relatives:
Rules of thumb for total shared cM:

What can DNA tell us?

The big 3 DNA companies

New competitors are emerging: Living DNA, MyHeritage
Part of
Autosomal DNA only
Very limited analysis tools
Overcharges non-U.S. customers
Full access requires paying ongoing annual subscription
Internal messaging system
Reached 1 million samples in July 2015; 2 million samples in June 2016; 3 million samples in January 2017
Most people use pseudonyms or initials
My results
Concentrates on medical aspects of DNA
Autosomal DNA plus predicted Y-DNA and mtDNA haplogroups
Overcharges non-U.S. customers
One-off payment
Optional internal messaging system
About 1 million samples
Most people anonymous
Analysis tools for non-anonymous matches
"Preparation for the transition to the new 23andMe experience" (including doubling of prices) started in October 2015 and still ongoing as of April 2017
Surname View
FamilyTreeDNA (FTDNA)
Dedicated to genetic genealogy
Autosomal DNA (Family Finder) plus various Y-DNA and mtDNA products
Good analysis tools
Single worldwide price
One-off payment
No U.S. bias
Simple e-mail communications
862,717 records as of 3 April 2017
Most people use real names: but married women recommended to use maiden surnames
Projects - e.g. Clare Roots and surname projects
My results

What do you get for your money?

The third-party sites

Levels of involvement

Lists of names
A black box algorithm can be used to list the names of those in a database whose autosomal DNA is closest to yours. 
You can look at your matches' own names, their ancestral surnames, ancestral placenames and family trees, if they have made these available.
Anybody can do this.
Lengths of half-identical regions
To get full value from one's investment in DNA analysis, one should move on from the purely qualitative approach of looking at names and take a more quantitative approach.
The first step is to look at the centiMorgan lengths of the regions on which one is half-identical with a potential relative.
The higher this percentage, the closer the relationship is likely to be.
Some basic arithmetic skills are required for this.
Locations of half-identical regions (phasing and triangulation)
This may exercise your brain cells a little more than the first two approaches.
Raw data
Sooner or later, the only answer to a particular DNA puzzle will be to look at one's raw data, in the form of long sequences of pairs of As, Cs, Gs and Ts, in order to work out exactly how and why something happened.
This is for the specialist. There are many of us around, willing to help.
Whatever level of involvement you choose, you have a responsibility to provide your DNA matches with at least an outline pedigree chart showing your direct ancestors (FamilyTreeDNA, AncestryDNA).

The easiest way to do this is to upload a GEDCOM file from your desktop genealogy software, e.g. Ancestral Quest.

Example I: The Kellys of Glascloon

We have at least five possible children of one or more Thomas Kellys with possible Glascloon connections:
Whose DNA do we have?
What do the comparisons tell us?
So Malachy, Anne, Nora and Bridget must be closely related:
Other evidence suggests that there may have been up to 10 Kelly siblings, born about 1816-1841.
Albert Greene's pedigree implies that their mother was Mary Green.
A triangulation involving two of the Kelly descendants and a Green descendant would confirm that the most recent common ancestral couple of the Kellys descendants were Thomas Kelly and Mary Green (see next example).
Finding that triangulation requires getting all the Kelly descendants to copy their results to
If you are not convinced that your theory is correct, just look for one more piece of evidence.

Example II: My Lynch ancestor was Irish - what townland was he from?

Example III: The Talty millions - did all of those entitled to it get their inheritance?

My greatgrandfather Old Johnnie McNamara was one of the supposed heirs to the Talty Millions in the late 1920s. But did they find all the first cousins?
So I am happy to conclude that Alan is my fourth cousin once removed. And Bridget in Australia (or her daughter, if she had died) was apparently just as entitled to a share in the Talty Millions as her first cousin/my greatgrandfather. But ...

Example IV: West Clare ethnicity

Conclusion: Why you should submit your DNA

Further reading