Genetic Genealogy

Irish Family History: Intermediate level

6 p.m. Tuesday 11 February 2025 and Tuesday 18 February 2025 (via Zoom)

by Paddy Waldron

WWW version:

http://pwaldron.info/TCD/intermediate/2025

Recordings:

11 February (video; chat); 18 February (TBA)

Outline

Review of beginners' session: the four components of DNA and their genealogical uses


 male offspring female offspring
sperm Y chromosome X chromosome
22 paternal autosomal chromosomes
egg X chromosome
22 maternal autosomal chromosomes
mitochondria
DNA component Inheritance path Inherited by
Y chromosome From father only (and only if male) males only
autosomal chromosomes (autosomes) Equally from both parents everyone
X chromosome(s) Unequally from both parents males x1, females x2
mitochondrial DNA From mother only everyone

Genealogical uses of mitochondrial DNA

Genealogical uses of X-DNA

Genealogical uses of autosomal DNA

Genealogical uses of Y-DNA

The rest of this course will look in more detail at the more widely used autosomal DNA and Y-DNA.

Preliminaries: Identity v. Anonymity

The trade-off

Basic guidelines

The basic guidelines for successful use of the DNA websites include the following:
Reveal the DNA subject's birth surname:
Most people inherit DNA with their birth surname, so identify yourself as a minimum by your birth surname with an initial or a title, e.g., P Waldron or Mr Waldron or Miss Durkan.
Reveal the chromosomal gender of the person who provided the DNA sample:
A woman does not have a Y chromosome, so may ask a male relative with the relevant surname to swab:
    a father, brother, nephew, cousin, etc., if her interest is in her maiden surname; or
    a husband, son, brother-in-law, father-in-law, etc., if her interest is in her married surname.
Valuable additional inferences can potentially be drawn once it is known whether two X chromosomes (female) or one X chromosome and one Y chromosome (male) are potentially available for comparison.
You must NOT attach a female name or a female's pedigree chart to a male DNA sample (or vice versa), as this causes untold confusion.
Be especially careful not to inadvertently link a male's Y-DNA results with a female's autosomal DNA upload at FamilyTreeDNA.com where error-checking does not look for this.
Avoid providing irrelevant information:
Your first name, married surname, adopted surname or marital status reveal nothing about your DNA, so you may keep these private if you wish.
You will get tired of explaining that you have no genetic ancestors with your married and/or adopted surnames.

Avoid pseudonyms:
They reduce the chances that your matches will bother to look at your family tree, contact you or share the information about your ancestry that they have and that you do not have.
Be consistent and avoid unnecessary confusion:
A real example (further anonymised):
Keep all your DNA-related correspondence in a single searchable email archive
Use the internal messaging system and AncestryDNA/MyHeritage/23andMe/LivingDNA or Facebook messages only to exchange email addresses.

Autosomal DNA: Managing your matches

Autosomal DNA: Fishing in all the gene pools

There are a growing number of DNA comparison websites and those interested in finding long-lost relatives should be in all of them, especially the largest ones.

Remember Murphy's Law of Genetic Genealogy, coined while I was helping an adoptee who is married to a Murphy:

If there are N DNA comparison websites and your DNA is in N-1 of them, then your most important match will be in the Nth.

In the words of another widely used metaphor, there are many online gene pools out there and there are many people who are in only one or two of them; for maximum effect, particularly if you are trying to find an unknown ancestor who has left no paper trail, you must fish in all of these pools.

You must spit for the websites which do not allow data uploads:

You must download your data file from the website of whichever laboratory (or laboratories) you use and upload it to the websites which do allow data uploads:
You must link your DNA kit and your pedigree chart and share them on the major autosomal DNA comparison websites:

Your WikiTree.com pedigree chart can be linked to your GEDmatch and 23andMe kits:

As of 11 February 2025, I have:

There are also mechanisms that could be used for marking known relatives at LivingDNA (Matchbox) or GEDmatch (Multi Kit Analysis/Tag Group Selection).

More matches can arise both from larger databases and from less strict matching criteria.

A higher proportion of known relatives can arise from smaller match lists, better genealogical tools, more effort by the researcher, etc.
Add DNA information to your genealogy database:

Add genealogy information to the online DNA databases:

AncestryDNA tools

MyHeritage.com tools

FamilyTreeDNA.com tools

Autosomal DNA: shared matches, triangulation and phasing

An autosomal DNA match between W and Z is defined by a list of half-identical regions (HIRs), e.g.

Chr B37 Start Pos'n B37 End Pos'n Centimorgans (cM) SNPs Segment threshold Bunch limit SNP Density Ratio
2 13,913,190 33,668,178 23.6 4,645 172 103 0.38
3 171,684,515 189,106,781 28.8 3,853 211 126 0.36
4 149,733,739 177,340,086 29.0 5,258 192 115 0.36
6 37,548,744 43,836,930 11.5 1,747 210 126 0.42

Shared, or In Common With (ICW), matches

A group of three or more individuals who all meet the relevant matching criteria with each other are likely to share a recent common ancestor (or, more often, ancestral couple).

The matches shared with a new match are usually the first clue to solving this puzzle of assigning the new match to an ancestor.

All of the DNA comparison websites allow one to identify the shared matches of two individuals in some form or another.

The matching criteria vary from one DNA comparison website to another.

The stricter the matching criteria, the more significant the shared matches.

FTDNA Family Finder

To find the shared matches of two individuals who match each other:

You will eventually identify a group of individuals, all of whom you suspect descend from a single common ancestor (or ancestral couple).

To see whether up to 10 individuals who match you also match each other, add them to the Selected Matches box on the Family Finder - Matrix page

To find the shared matches and shared cM of two or more individuals who belong to the same project, whether or not they match each other, it was formerly possible to:

However, the shared matches option was removed from this menu in 2021 and it is unclear whether or when it may be restored.

AncestryDNA

On each match page, there is a Shared Matches or Shared Matches PRO link, depending on the subscription paid (or not paid). (Screenshot.) (ScreenshotPRO.)

Hence:

Matches are sorted by closeness of relationship to the logged-in individual.

GEDmatch

To find the shared matches of two individuals, whether or not they match each other, use the "People who match both, or 1 of 2 kits" tool on the main menu.

This lists shared matches of Kit 1 and Kit 2, but the user sets the cM threshold of largest segment and cM threshold of total matching segments.

Matches are sorted by closeness of relationship to Kit 1.

To sort by closeness of relationship to Kit 2, re-use the tool with the kits in reverse order.

The Multi Kit Analysis menu (now available only to Tier 1 subscribers) can run an Autosomal Matrix Comparison on up to 100 kits.

MyHeritage

When the Review DNA Match page eventually completes loading, the Shared DNA Matches section:

Matches are initially sorted by Total shared DNA (the sum of the centiMorgans shared with the two individuals), but can be re-sorted. 

A can see not only that B matches C but also the cM shared by B and C.

A's shared matches with B will be exactly the same as B's shared matches with A, initially in the same order.

Triangulated matches

Triangulation and phasing are really opposite sides of the same coin.  If V is half-identical on the same region with W and Z, then there are two possibilities:

  1. W and Z are half-identical to each other on this region, in which case V, W and Z probably inherited an identical segment in this region from a single common ancestor and the relationship can be described as triangulated; or
  2. W and Z are not half-identical to each other on this region, in which case V is probably related to W on V's paternal side and V is probably related to Z on V's maternal side, or vice versa, and V's autosomal DNA in this region can be phased.

Overlapping matches can represent:

Triangulation groups

The ultimate objective is to collect DNA matches into triangulation groups. A triangulation group is a set of three or more people who are all half-identical to each of the other group members on overlapping regions.

The more individuals who are added to the triangulation group, the smaller the overlap may become.

A triangulation group of three or more individuals are very likely to share a recent common ancestor (or, more often, ancestral couple).

The triangulated matches that I share with a new match are usually the second clue to identifying through which of my most distant known ancestors I am related to the new match. Some of the DNA comparison websites allow one to identify the triangulated matches of two individuals in some form or another.

FTDNA Family Finder

One had to be a little devious to find triangulated matches directly at FTDNA.

The Linked Matches feature (previously known as Assigned Relationship and before that as Linked Relationship, and currently hidden on the "Sort by" menu) 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).

AncestryDNA

AncestryDNA refuses to provide any way of identifying triangulated matches.

MyHeritage

MyHeritage shared match lists include a symbol identifying which of these matches are triangulated.

Make sure that you have not opted out of showing shared segments.

There appears to be no way to filter the list of shared matches to show only the triangulated matches.

LivingDNA

GEDmatch

Assigning DNA matches and DNA segments to ancestors

For every autosomal DNA match, and for every autosomal DNA half-identical region, one would like to assign both to an ancestor. In particular:

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:

For example:

My own family tree has numerous recent complications which force me to think in terms of individuals rather than couples:

Matches who are not known relatives can be tentatively assigned to ancestors (or predicted) based on

I recommend using:

One can use similar methodologies on all the websites:

A counter-example

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.

Consider these three marriages in the United Church of England and Ireland (the established church) in Kilkeedy, County Limerick: However, these close triangular marriage patterns are very rare.

You may still find two distant relatives, related to you through two different ancestors, appearing as shared matches, because they are descended from a third common ancestral couple whom they share with each other, but whom neither shares with you.

Other third party tools and websites

The major DNA websites do not like the load imposed on their servers by the more powerful tools designed by third party developers.

Y-DNA and surname projects

Men and our surnames are defined by genetic signatures comprising chronological sequences of SNP mutation labels like:

which have superceded the original Simplified Tree of Y-Chromosome Haplogroups.

FTDNA currently gives:

The sequence of SNPs can be explored by:

FTDNA uses the CE/BCE notation in place of the AD/BC notation for its estimated years.

Further reading