Hands up if you’ve taken a DNA test for family history purposes – or out of simply curiosity – and now have no idea what to actually do with it! Don’t worry you are not alone and I’ve got you covered with this fact packed article.
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DNA For Family History Doesn't Have To Be Confusing
Don’t worry if (at first) you don’t understand all the DNA science. I didn’t. It can take a while to wrap your head around some of the more complex details. I started by reading Wheaton Surname/Beginners Guide to Genetic Genealogy.
I understood a small fraction of the text but I kept re-visiting it once I was actually working with DNA in practice.
Re-watching and re-reading DNA information is important. Each time you watch you’ll take on a little bit more information. Do this in conjunction with actually analysing and working with your matches. Combining your learning with actual practical application is important. It’s a bit like reading how to knit – it’s not the same as actually doing it.
How Much DNA Do I Share With My Match?
To get started with DNA for family history all you really need to know is that your DNA matches will share some DNA with yourself. The amount of DNA you share is measured in CentiMorgans, abbreviated as cM and you share cM over segments.
Understanding Segments of DNA for Family History
Imagine cM as a measurement on a ruler. You have a ruler and so does your match. Sometimes you and your match will both share cM from numbers 0 to 10 on your rulers. Other times, you’ll share cM between 0 to 10 and then your DNA at 11 to 15 is different. But, your DNA at 16 to 25 matches again. These areas of matches are segments. So sometimes, you’ll see shared DNA expressed as 50 cM & 2 segments. Sometimes, you might even see something expressed like, “50 cM shared over 2 segments with the largest segment being 40 cM”. This means you share one piece of DNA that runs for 40 cM and then the other 10 cM you share is in another segment.
Small segments of shared DNA indicate a more distant relationship between you and your match. In fact, DNA matches with segments under 7 cM might even be “false positives”. In other words, it’s chance you share 5 cM over 1 segment. There are areas within our DNA whereby we are more likely to share DNA with others – these are sometimes referred to as “common build up” areas. See: https://thegeneticgenealogist.com/2017/12/29/a-small-segment-round-up/
Using CentiMorgans of DNA For Family History
The amount of cM you share with an individual is a good indication of their relationship to you. There’s a great tool on DNA Painter that can tell you the possible relationships between you and a DNA match based on how much cM you share. It’ll also tell you the likelihood for each relationship in percentages. Ancestry’s own relationship charts are now based on the data behind this tool.
Personally I like that the chart that DNA Painter uses to show your various relationships includes information on the range of cM that you “could” share on each of the predicted relationships.
Note: The way in which your cM is measured varies across the different testing sites so don’t panic if you have done tests across sites and have identified common matches but you seem to share different amounts of cM depending on which site you look at. The DNA Painter works across all the sites.
Your Cousins Don't All Share The Same DNA
So now we’ve established DNA is measured in cM across segments, you need to understand that what you share with your cousins will vary. You don’t share the same amount of cM with every 2nd cousin. You’ll have a range and sometimes your cousins won’t match each other – even though they both share DNA with you.
Within the first week of getting my DNA results, I was totally confused. I had three distant cousins descended from the same ancestor as myself. All three were in my list of Ancestry matches. However, after contacting the matches I realised that the cousins themselves did not all match with each other.
This really took me some time to get my head around. How could we all be descended from the same person if we didn’t all match each other? The answer is glaringly obvious. I’d already read the answer in the multiple science / explanation websites that’d I’d browsed. But reading something, understanding it in the moment and applying it in practise are not the same thing!
I’m going to share with you the explanation that finally made ‘how we inherit’ DNA click for me.
DNA is like a pack of cards
Imagine DNA as a pack of 52 cards. Everyone has 52 cards, and everyone gets half of these from Mum and half from Dad. That means out of the 52 cards your Mum holds, she’s given you a copy of half of those in her hand. But, this is a shuffled pack. Each time a new baby is born, Mum and Dad both re-shuffle their cards before handing them out.
Your maternal great-great-grandmother, Mary had lots of children and multiple grand-children. Amongst her cards she had the Ace of Spades, the Queen of Clubs and the King of Hearts. Through the generations your Mum ended up inheriting the Ace and the Queen. But she did not inherit the King.
Now, when your Mum took her cards, shuffled them and gave you half – you happened to inherit the Ace of Spaces. This means you will match with any of Mary’s other descendants that also inherited the Ace of Spades.
When your Mum had your brother she shuffled her cards and gave him half. He got lots of the same cards as you, but he didn’t get the Ace of Spaces. Instead, he inherited the Queen of Clubs. Now he has matches with the descendants that inherited this card from Mary. Matches that you don’t have – because you didn’t inherit the Queen.
You have a DNA match descended from Mary that matches both you and your brother. That’s because this match inherited both the Ace of Spades AND the Queen of Clubs.
There are other cousins you’ve identified through paper research but neither you nor your brother are genetically matched to them. That’s because they inherited (for example) the King. A card that did not pass down to your Mum and therefore couldn’t pass down to you.
The random nature of DNA is why asking as many family members as possible to take DNA tests can be so helpful. Imagine if one of Mary’s descendants took a DNA test and had the King. If she shared her DNA matches with you, you’d have a whole new set of Mary’s descendants to explore.
An alternative analogy
DNA is like a pack of M&M’s, you never know what random collection of colours you are going to get. The more packs of M&M’s you buy the better your chances of getting some “blue” sweets. Similarly, the more relatives you test the more likely you are to discover a strand of DNA that matches with another descendant of that elusive ancestor you’re trying to find out more about.
What Are DNA Matches & How Can I Use Them For Family History?
Once you’ve received your DNA results you’ll be able to view a list of matches. These are all people that share some DNA with you. By default most companies list them by the amount of shared cM (in descending order) – so generally closest matches are at the top of the list.
On Ancestry you can link your DNA to your family tree (public or private) and if you are lucky you might have some ‘Thurlines’.
This neat bit of matching tech takes information across trees from multiple users and tries to suggest how you are related to your matches. It can be incredibly powerful. However, it should be taken with a BIG pinch of salt. As we all know, just because something is in a user’s tree doesn’t mean it’s correct.
My Heritage has a similar system for suggesting how you might be related to a match. Again, take it with a pinch of salt. Check the workings!
Reviewing all your matches is a huge undertaking. Some matches are inactive, dead accounts, some have private trees, some have no trees at all.
BUT the results can be well worth the pain. Finding matches help you take your family tree further back in time and more importantly perhaps, matches can provide you with more stories. I’ve found photos of my ancestors, inherited by other lines of my family – one’s my line had long lost contact with. I’ve found out that my ancestors had siblings that I hadn’t known about AND even children I didn’t know about!
Similarly analysing DNA matches for family history purposes can lead to parentage discoveries. As in, identifying previously un-named father’s for those illegitimate ancestors.
Filter DNA Matches To Refine Your View
The below is written presuming you took a test at Ancestry but other test providers have similar systems.
The very first task you should undertake is to start to colour code your matches into groups. This works even if you only know one side of your family tree. For example, if you only know your maternal line then colour code all the matches you can definitely define as “maternal”. You could colour them pink (a stereotype, I know) and label them “Maternal”.
Now when you want to try and narrow down your search for your paternal line you can filter out the ‘maternal’ matches.
For adoptees, you might want to try to start grouping and filtering matches by location. Then search for common surnames amongst those clusters of locations.
Matches can belong to multiple groups and have multiple colour codes. You can also “star” matches to help you identify matches you really want to look at in close detail later.
Don't Rely On Shared Surnames
When looking at your shared matches you may start by trying to determine whether you have a shared surname – but don’t forget to check shared locations. I have lots of Williams and Davies in my family tree – as do many of my matches. But my Williams and Davies come from distinct areas in Wales. I’m more interested in matches that share ancestors from the same location than the surname itself – especially as some of my ancestors were illegitimate. That’s where utilising for DNA for family history really can open new doors.
Build Quick And Dirty Trees To Utilise DNA For Family History
You’ll soon find lots of matches that only have tiny trees. You might have to build these trees out yourself in order to find a surname that’s either in your own tree – or in the tree of several of your other matches (and therefore warrants exploration).
It’s best to start this by making a private, unsearchable tree. Use Ancestry’s hints and public trees to do the initial work. It’s just about the only time I’d say to dive into unsourced trees and to ignore the normal double checking rules!
Once you’ve found a possible connection – go back and reassess each part of the tree. If there are areas that are dubious or lacking in sources then bear this in mind but don’t let it stop you from reaching out to a possible contact.
It’s important to note that you are contacting DNA matches saying you think this is how you are related. Your not saying you’ve proved it (unless you really have).
Google and Social Media Are Your Friends
Many of your DNA matches will not have public trees. You can try messaging these matches but some will never respond.
You can use other techniques in order to try to identify the match. For example, try googling their user name. Perhaps they’ve used it elsewhere, like on a genealogy forum?
You can also search by name and location on Facebook. I’ve identified matches before by finding their Facebook profile – handy if they have a pic that they’ve also used on their profile within a testing site.
Your DNA is For Your Family History So Record Your Findings
Remember that DNA is no different from any other aspect of your family history. You need to record your findings! Including your sources.
Now don’t get me wrong, to start with you need to make sure you add notes directly to your DNA matches. That way you can view them as you are working, directly on the screen. But think of these as bullet points or notes in brief.
You’ll also need to keep detailed notes in either a research log, a spreadsheet or a family tree package. Whatever works for you. Don’t forget to include information on who you’ve contacted, why, when and whether they replied!
Don’t be afraid to trace downward on your family tree, up to and including your matches. This could be as simple as keeping a private “quick and dirty” tree on Ancestry in order to easily record how you are related to your DNA matches in a visual manner. Just make sure that if you aren’t able to fully source your tree that you make it private and unsearchable – that way it won’t be copied by those that just say yes to all hints.
DNA Matches: Triangulation, Surnames and Locations
Looking at the matches you share with your match (known as ‘shared matches’) can also help. These are people that share DNA with both yourself and one of your matches. Sometimes a good match might not have a public tree, but one of the matches you both share might – and this can provide clues as to how you are related to the user that’s missing a tree.
You’ll probably still need to contact the user without a tree, but at least you have an opening gambit – “hello, is it possible we are connected via surnames X, X and X” is a lot more engaging than “hello, we’re connected somehow, can you look at my tree or do you have an online one I can view?”
Similarly, if you identify one of your matches as being descended from a particular couple (say your paternal great-great grandparents) then the chances are high that all the matches you share with that person are either descended from that couple OR they are descended from one of your great-great grandparents ancestors.
You could colour code them as such and then use filtering to either work on this collection of matches – or remove them for when you are looking at different groups of descendants.
Chromosome Browsers for DNA
Note: Ancestry doesn’t have one! But you can load your DNA onto other testing sites in order to take advantage of their tools.
Loading your results onto other sites has two benefits. One, your widening the net of matches you have and secondly you can utilise tools available at different sites, such as chromosome browsers.
Please read the terms and conditions, and privacy notices of all websites, and ensure you (or the DNA test taker) is happy, before you upload. Some sites, such as Gedmatch (a free site) have had some rather bad press recently due to data breaches, sharing DNA with police etc. Make sure you read up and make an informed decision about which sites you are happy to use – and which you are not!
Now back to chromosome browsers. These are DNA tools for family history that enable you to see where within a chromosome you match a distant relative. can help with triangulation – if a group of shared matches all match across the same part of a chromosome then there’s a good chance they are all descended from the same person.
Let’s hop back to our ruler analogy. This is a massive simplification of genetics, but hey it helps! You have 23 pairs of rulers, imagine them in pairs like the pic above. One ruler in each pair is inherited from your Mum and the other from your Dad. Then you have 1 extra ruler (that’s your sex chromosome – your X or Y). If you are female you have a X inherited from your Mum. Boys get a Y ruler.
The only problem is none of the DNA testing companies can tell you which ruler (your Mum’s or your Dad’s) is which. In other words, they’ll tell you that you match on one of your rulers (and how many cM & segments) but not whether that’s the ruler you inherited from Mum or Dad.
My Heritage and Gedmatch, amongst other sites, include a chromosome browser for each of your matches. This can be in the form of a visual image for each of your matches, or a table showing shared data. But wouldn’t it be great to see the shared DNA of several matches all in one place? Even better, if you mapped the shared DNA of known matches couldn’t this then be used to help you work out your connection with unknown DNA matches?
In other words, if I could see the DNA of my grandfather, wouldn’t I then be able to see if someone else’s DNA might matched his?
This can all be achieved using DNA Painter. This site allows you to create a free profile, allowing you to load your shared DNA data to create a visual image of your DNA map. It sounds complicated but it’s really easy. Just give it a try yourself!
DNA Painter have also recently launched a tool called What Are the Odds? (WAO) that can be used to test hypothesis regarding how you might be related to a match. It’s amazing, but complex so I’ll save that for another post.
There are lots of different systems or methods for recording and tracking your DNA matches for family history. I strongly suggest joining the Facebook group – Genetic Genealogy Tips and Techniques, created and managed by DNA guru Blaine T. Bettinger. This group is full of fantastic suggestions and methodologies. For example, using shared matches and colour coding to work out relations – called The Leeds Method. It’s also worth keeping an eye on Bettinger’s blog, The Genetic Genealogist and the ISOGG Wiki.
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