Using DNA for Genealogy by Malcolm Houston – March 2019
Levels of interest have increased significantly in family history societies over the last few years, as more and more genealogists are starting to use DNA testing as a part of their family history research.
Due to technological advances and affordable prices, DNA testing is now becoming widely used to confirm family lines and connect with biological relatives.
You may want to discover branches of your tree not found through regular research, confirm or disprove family relationships, find cousins with whom to share research & photos, see if persons who share your surname are related, discover your ancient origins, potentially solve long-standing research ‘dead-ends’, explore the validity of family stories, identify previously unknown close family (e.g. adoptees searching for parents), or you may simply be curious to see what your DNA reveals.
Don’t let the scientific nature of DNA scare you off, as once the basic test types are understood, the minimum technical know-how required is the use of email and messaging in order to contact your DNA matches.
Collaborate with your new-found genetic relatives using your traditional genealogical skills to determine your ancestors-in-common.
A DNA kit is ordered online from one of the major DNA testing companies.
Your test kit arrives by mail or courier within a few days to a few weeks, depending on company.
The DNA tests themselves are very simple to use:
- a cheek swab for Family Tree DNA, MyHeritage or Living DNA
- a saliva sample for 23andMe or AncestryDNA’s kit
After testing, you simply post your sample back in the pre-addressed envelope or package.
All notifications are via email and results are provided via an online account.
Once your DNA has been tested, your results are added to a very large database and you access them via your online account (nothing is sent by mail).
Even if you have no close matches initially, large numbers of people are testing each week globally and you will continue to receive new people matches regularly.
Your online account is also used to keep track of your order status, to enter your family tree and ancestral surname information, to join projects, to see your results and which people you match, to manage your profile and tree settings, and to download a copy of your DNA raw data file (for use with additional tools/sites).
A centiMorgan (cM) is a unit of measure for DNA. It tells you how much DNA you share with another match. In general, the more DNA you share with a match the higher the cM number will be and the more closely related you are.
There are several different types of DNA that can be tested for genealogical purposes:
Males inherit a y-chromosome from their father, through his father, his father, his father, etc., on the direct paternal line, as per the blue boxes on the chart below. Examples of how Y-DNA testing can be useful in your family history research include:
- 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 (e.g. 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
Which husband of a female ancestor who married more than once was the father of particular children (e.g. surnames of young children may have been changed)?
- In combination with autosomal testing, it can help determine if previously-unknown cousin matches might be related on the paternal side of the family – or at least help by disproving relationships.
Only males have Y-chromosomes, so only males can take a Y-DNA test.
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.).
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 (e.g. father, brother, uncle, cousin) to determine their paternal ancestry.
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 (e.g. 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.
Everyone inherits mitochondrial DNA from their mother, through her mother, her mother, her mother, etc. on the direct maternal line, as per the pink boxes on the chart below. Examples of how mtDNA testing can be useful in your family history research include: –
- Connecting maternal lines where no paper/traditional records are available.
- Determining if two females with the same surname were related (e.g. if living near each other).
- Determining if females in different locations but with unusual maiden surnames were related.
- Determining the earliest known origins of a maternal line, by connecting with matches who have researched their line further back.
- Research hints: if your most distant known maternal ancestor has an unknown maiden name, an exact FMS match in her place of origin might provide clues for that missing maiden name.
- Research hints: if your autosomal DNA matches share a mtDNA FMS haplogroup with any of the tested mtDNA lines on your pedigree, hone in your research on those particular direct maternal lines.
- Maternity questions: Do siblings have the same mother? Do cousins share the same maternal grandmother? Which wife of a male ancestor who married more than once was the mother of particular children? In combination with autosomal testing, it can help determine if previously-unknown cousin matches are related on the maternal or paternal side of the family – or at least help by ruling out particular relationships.
Both males and females inherit mitochondrial DNA from their mothers, but only females can pass it on to their children.
If a person has an exact match on their mtDNA with another person who has tested (at the Full Mitochondrial Sequence level), it indicates that they descend from the same female somewhere back in time – but it can’t necessarily tell you where and when, as the mtDNA can remain unchanged for many generations, even hundreds or thousands of years. So an exact match could be related very distantly, but could also be a very close maternal line relative… it all depends on who has done the FMS test and is it in the matching database.
The pedigree chart below shows (in pink) people who could potentially share the same mtDNA as you – providing there are no non-maternal events, such as adoptions, in the direct maternal line.
A person could potentially share a mitochondrial DNA match with a descendant of any direct-line female in the pedigree, going back many hundreds of years, not just the generations shown in this chart. Males shown in pale pink also have the same mtDNA, but cannot pass it on.
Cousins identified with gold stars can be male or female, as their mothers are direct female descendants and pass their mtDNA on to them.
You are not restricted to testing the mtDNA of your own maternal line. You can test your father or any of his siblings to discover the mtDNA of his mother’s maternal line. If you can find a willing relative who descends from any other direct maternal line in your tree, you can test their mtDNA to investigate that line genetically too. The person you test can be male or female, as long as their mother directly descended through that particular maternal line of interest. In the chart below, for example, you could test your father, a paternal uncle or a child of a paternal aunt to determine the mtDNA of your paternal grandmother’s maternal line.
Autosomal DNA is inherited from all ancestral lines, so anyone can be tested and your matches may descend from anyone on your pedigree chart, up to about 6 generations back (but may be further).
Everyone inherits autosomal DNA from their parents: 50% from each parent, which contains a random mix of DNA segments from their parents, their parents, their parents, back for several more generations.
The wonderful feature of autosomal DNA is that it can be inherited from all lines of your pedigree, not just the direct paternal or maternal lines. Anyone can test their autosomal DNA – any age, any gender – and it is quick and easy to do, via a cheek swab or saliva sample.
Any one of your ancestors in the pedigree chart below could have passed some of their DNA onto you, and to other descendants as well, even quite distant cousins.
If both you and other descendants of the same ancestor’s test with the same company, and share a minimum-sized segment of DNA in common, you should show up in each other’s list of matches.
Consider that even if you only go back six generations – to your 4th great grandparents as in the chart above – depending on how many surviving children each couple had, you could potentially have tens of thousands of 5th cousins however not all of your distant cousins will be detected as matches to you.
The chart below shows the likelihood of detecting cousins who have tested at the same company:
Sources: Family Tree DNA and 23andMe and AncestryDNA.
Each parent can only pass down half of their autosomal DNA to each child, so each child will get a random mix of segments from their parents, and consequently a random mix from each grandparent.
The diagram below demonstrates how the DNA can be recombined at each successive generation. Three children of the same parents can get quite different mixes of DNA from their grandparents, which means they will match relatives and cousins slightly differently.
For 3rd cousins and further back, some of your tested cousins will be detected as matches to some siblings, and not detected by other siblings. Testing siblings is a very good idea to get DNA matches with a wider selection of cousins. If you don’t match a 3rd cousin as expected, test one of your siblings or your cousin’s siblings, as they might match each other.
Your genetic genealogy project will progress rapidly once you test some known cousins and/or confirm new cousins, as being able to identify your most recent common ancestors helps you isolate those lines you share with other matches in common.
It is also highly recommended to test older generations, if possible, as their DNA will be less diluted than the younger generations. Testing their DNA can also help isolate your other matches to your shared branches. If you are young enough to still have grandparents, great aunts, great uncles, or cousins of your grandparents, you are very lucky and would be wise to test them while you still can (DNA tests for birthday presents are a great idea!).
Relationships are estimated based on the percentage of shared DNA, e.g. 50% for a parent, child or sibling; 25% for a grandparent/grandchild, aunt/uncle, half-sibling, niece/nephew; 12.5% for a great-grandparent, 1st cousin, great aunt/uncle; 6.25% another generation removed, etc.
The International Society of Genetic Genealogy (ISOGG) Wiki contains some useful charts for estimating autosomal DNA matches based on the percentage of DNA shared, or the measure/quality of the segment shared (in centiMorgans – cM).
The chart below shows the average amount of autosomal DNA inherited by all close relatives up to the third cousin level:
http://www.isogg.org/wiki/Autosomal_DNA_statistics (Chart: Dimario, Wikimedia Commons)
The following table, from the same ISOGG link, estimates relationships based on the average amount of autosomal DNA shared:
Autosomal DNA testing does not ‘find or identify’ relatives as such, but matches testers with other people who have also tested with the same company. It is purely a matching system – the more people that test, the more matches everyone gets, including with previously unknown cousins. It is a big puzzle… you are given the clues which are the genetic relatives, and you have to use your genealogical research skills to find the records and evidence to connect them.
Traditional ‘paternity testing’ tests two specific individuals and compares a very small number of unique markers to see if they matched each other. If not, the process is repeated with two new candidates (if any are available), and often at a significant cost.
With genealogical DNA testing, approximately 700,000 markers are tested and compared with those of hundreds of thousands of other people in the database.
Testers are given a list of people who share DNA with them, with the closest predicted relatives at the top of their match list. It is impossible to know before testing if you will get any close matches.
Most people tend to start with a selection of 2nd-4th cousins at the top of their match lists (FTDNA’s Family Finder), but some people can get closer matches – it all depends on which of their relatives have already tested.
If the person you are testing is an adoptee, donor conceived, a foundling, or has unknown parentage for whatever reason, it is recommended that they test with all three of the genealogy DNA testing companies, to get their DNA into all three databases to have the best chance of matching with others (in case the person they want to match with has tested at a different company).
Testers at any of the three companies can also upload a copy of their raw data (results) to a free site called GEDmatch.com, where they can be compared with others who have tested at other companies and also uploaded their results. GEDmatch is not a replacement for testing at all three companies, as only a small proportion of testers from each company upload their results, but it is a great site with a wide range of useful tools.
X-chromosomes follow specific inheritance patterns, which are different for males and females. If you share X-DNA with a match, your shared ancestors will be restricted to particular lines of your pedigree.
Practical uses of X-DNA
- If a male shares X-DNA with a match, then the ancestor in common will be on his mother’s ancestral lines, according to the X inheritance patterns in the ‘Male’ charts.
- If siblings have tested their autosomal DNA, and a brother has X-matches in common with his sister(s), then the sisters will know that those particular X-matches must have come from their mother, as their brother could only have inherited them from their mother
- If brothers share very little X-DNA with each other, one would have inherited most of his X from his mother’s father and the other would have inherited most of his X from his mother’s mother, or they inherited the exact opposite of a recombined X.
- If brothers share most of their X-DNA, they would have inherited it either from the same maternal grandparent, or the same or very similar recombined X from both maternal grandparents.
- If half-sisters with the same mother share very little X-DNA with each other, one would have inherited most of her X from her mother’s father and the other would have inherited most of her X from her mother’s mother, or they each inherited the exact opposite of a recombined X.
- If half-sisters with the same mother share most of their X-DNA, they would have inherited it either from the same maternal grandparent, or the same or very similar recombined X.
- A daughter will share a whole X chromosome with her father.
- Full sisters will share a whole X chromosome, from their father.
- Half-sisters will share a whole X chromosome if they have the same father.
You can attribute X segments to particular grandparents by comparing your X-DNA with cousins and other close relatives from each side of your family.
Autosomal DNA tests include an estimate of your ethnic ancestry, including cluster maps and population migration maps showing where your ancestors came from hundreds or up to a few thousand years ago (sample at right: Family Tree DNA’s myOrigins).
In FTDNA, the map may also display pins showing the locations of your matches’ most distant known ancestors.
For those who are interested, other tools allow your DNA kit to be
compared with ancient DNA, such as Neanderthal.
23andMe in the US was initially a health reporting company that expanded into genealogy matching. No health reporting is available in Australia or New Zealand. Limited health reporting is available to residents of the US, UK, Ireland and Canada.
Autosomal DNA raw data from Family Tree DNA, 23andMe, AncestryDNA, MyHeritage DNA and/or Living DNA may be uploaded to www.promethease.com to generate health reports, for a cost of $12. Refer to the information and videos on the Promethease home page.
There are five major DNA testing companies for genealogy – Family Tree DNA, 23andMe, AncestryDNA, MyHeritageDNA and Living DNA.
Family Tree DNA is popular for testers from Australia & NZ, as it has a large international database, sells all test types, is very affordable, requires no ongoing subscription, hosts thousands of surname and geographical projects, and provides easy analysis tools.
23andMe has a large database, although testers are generally more health-focused rather than interested in genealogy. It has some great analysis tools and highly-regarded ethnicity results, but its compulsory international shipping makes it very expensive for Australians and New Zealanders.
AncestryDNA was previously US-only, but launched in Australia & NZ, UK, Ireland and Canada during 2015 and has now surpassed 14 million testers worldwide. Ancestry’s huge collection of member trees can be linked to DNA results to help identify relatives through Shared Ancestor Hints. Its DNA matching features work best with a subscription and a public family tree.
MyHeritageDNA is newer to DNA testing, but it has over 100 million members, so is growing very quickly and providing some great matches!
Living DNA breaks down your ancestry into 80 worldwide regions, including 21 British regions, Irish, German and Scottish regions.
Family Tree DNA hosts over 9500 projects, including for surnames, geographical regions, and haplogroups.
Australian Settlers DNA, Australian Convicts DNA, New Zealand DNA, British Isles DNA by County, Ireland Y-DNA and Ireland mtDNA are just a few projects that may be of interest.
Currently, the favourite test type amongst genealogists who don’t have a specific need to test the direct male or female lines is an autosomal DNA test. AncestryDNA, MyHeritage DNA and Family Tree DNA are the most popular, but review all companies to ensure that your goals and the pricing and features of all the genealogy testing companies before you buy, to ensure your choice suits your needs.
Expect to be matched with a range of biological relatives, up to 5th cousins back or further.
Once your results are released, you can start corresponding with
your matches and comparing trees and research to determine your shared
ancestors. As more people test, everyone’s chance of finding closer
matches improves. It is also very useful to test siblings and other
cousins, as they may share DNA with cousins that you don’t.
For beginners, there are plenty of free links and
resources. As you gain experience, there are third-party sites &
tools you can utilise to analyse your results and find additional matches.