Solving Adoption Mysteries with DNA

There are many people who don't know who one or both of their parents were, among them adoptees, foundlings, and donor-conceived children. For these people there is frequently a desire to track down their biological relatives and learn a little about their roots. Sometimes the person of unknown parentage is one of our parents or grandparents.

DNA has helped revolutionise our ability to trace birth families and this article describes how you can use it to help solve these kind of mysteries, identify birth parents, and connect with living relatives. This journey is an exciting one and an emotional rollercoaster so make sure you have your support network around you to help you each step of the way.

If you are the person of unknown parentage, you should put your autosomal DNA (atDNA) in all the major DNA databases currently available, in the hope that you will find your birth parents or one of their close relatives there. 

My favoured approach (Sep 2023) is to do your first test with Ancestry and once you have your results, you can download a copy of your DNA datafile to your computer and then upload it to several other databases for free, namely:

• MyHeritage … https://www.myheritage.com/dna/upload
• FamilyTreeDNA … https://www.familytreedna.com/autosomal-transfer
• LivingDNA … https://my.livingdna.com/signin
• Gedmatch … https://app.gedmatch.com/register.php

Leah Larkin has written some great step-by-step instructions for doing this on her website here.

There is one other major company you could consider testing with (23andMe, usual price about 99 euro) but only if you don't get sufficient close matches in the other databases.

At a later stage, if you need to do confirmatory DNA testing on potential close family members, simply use whichever of the above tests is the cheapest at the time (the various companies have frequent sales where the price can drop to as low as $49).

If you are very lucky, your atDNA results will include a very close match and you will be reconnected with your birth family in a matter of days or weeks. My good friend Winnie had been searching for her family for 40 years. At 76 years old, she felt she was running out of time. But within days of getting her DNA results, she found the son of her half-sister in the database and the following week she was reconnected with four half-siblings she never knew existed. And they welcomed her into the family with open arms and warm hearts. What an incredibly precious gift. You can see Winnie’s story on YouTube.




Most people don’t have such very close matches, but they are happening more frequently as more people join the databases. A 2021 survey found that they occur in about 15-20% of Irish & British cases. It’s more likely that your closest match will be a second cousin, or if you’re fortunate, a first cousin. Both of these scenarios are good news. What then follows is a sequence of steps to figuring out who is your common ancestor (or rather your common ancestral couple – because most of the time you will share an ancestral husband and wife in common).

Success Rates in Irish & British cases (2021) vs US cases (2016)
from Journal of Genealogy & Family History

Some people do this work on their own (because they want to, and have a good grasp of the technical aspects of the process). For those who need help, there are professional genetic genealogists who can provide assistance (some charge a fee), or there are volunteer genetic genealogists who can help free of charge - if you are interested in this option, check out the following groups on Facebook: DNA Detectives, Search Squad.

Here are the technical steps in the process.  Often, these steps are done in parallel rather than in sequence:

1. Check for a Quick Win

Is there a very close match at the top of your match list? Anything >700cM suggests a 1st cousin or closer. And if they have a good family tree available, you may be able to figure out who your parent is fairly quickly. And if that is the case, they will be able to see you too and the cat may be out of the bag very quickly. But if you are not ready to tell your story, you may wish to turn everything off i.e. privatise your account so that no one can see you as a match. Making yourself unseen and incognito allows you to create some breathing space for yourself, and give yourself some time to think about what you want to do next. You may want to see if you can find any of these new family members on Facebook just to see what kind of people they are. You may even find some photos of your parent or half-siblings. And then, when you are ready, you can attempt to make contact.

2. Cluster your matches into distinct genetic groups

Matches who match each other probably all share the same common ancestor. The goal here is to try to get at least four groups of "matches who match each other". Hopefully two of these four groups will be on your paternal side (one connected to you via your father's father and the other via your father's mother) and two will be on your maternal side (one via your mother's father, the other via your mother's mother).

I usually start with the first match below 200cM. On Ancestry, this involves selecting this first match, clicking on Shared Matches, and putting a coloured dot beside this first match and each match who matches you both. This creates the first genetic group. 

Then return to the main match list and repeat the process with the next match <200cM who doesn't have a coloured dot beside them. This creates the second genetic group. And then repeat the process for the third and fourth genetic groups. You will find that your closest matches will probably have several coloured dots beside them i.e. they belong to two or more groups.

Ancestry now have a handy feature that automatically separates your matches into Parent 1 and Parent 2, but does not tell you which parent is which. However, sometimes you can easily figure this out for yourself. In due course, they may be able to divide your matches into Grandparent 1, 2, 3 & 4. This would certainly make your research easier.

Other ways of figuring out which parent is paternal and which is maternal is to compare Y-DNA signatures Y-DNA is only passed down along the father father father line), or mtDNA signatures (mitochondrial DNA is only passed down the mother mother mother line), or the amount of X-DNA shared.

3. Identify the common ancestors for each cluster

Starting with the cluster with your closest matches, compare the family trees of everyone in the cluster and see if you can identify a common ancestral couple (or at least a common surname or ancestral location). I usually open each tree in a new tab (in pedigree view) so that I can rapidly go from one to the next and do a quick scan of the most distant ancestral surnames looking for surnames that repeat in several trees.

Sometimes a family tree is not available because your match has not shared it publicly online, so you will have to ask them nicely for it. And that means engaging them in a conversation initially and developing rapport and a trusting relationship with them over time. And this could take weeks or months because some people do not check their messages. I will usually send a brief but friendly initial message as a "way in" (see below) followed by several "nudge messages" over the subsequent months (e.g. "Hi Joe, just wondering if you have had a chance to read our previous message?"). 

Example of a brief, friendly initial message

Once you have identified the likely common ancestral couple, try and figure out at what level you are likely to sit within their tree. You can do this by assessing the amount of DNA you share with each member of the cluster. The Shared cM Tool can help you figure out your relationship with each match. It also has a handy Relationship Chart with the average amount and range of DNA shared for a wide variety of relationships from half-sibling to 7th cousin. Just enter the amount of DNA you share with a person and the Shared cM Tool will generate a list of possible relationships with probabilities for each one. You can probably rule out some of the possibilities based on the age of your match (if you can find it or figure it out) - for example, if you are 40 and they are about 75, then they are likely to be your parent's generation and thus would be a "once removed" cousin to you. For difficult-to-place cases, I use the WATO tool to generate the most likely scenario.

Be aware that the Shared cM Tool does not take into account double-connections e.g if you are related to a match via TWO ancestral lines (e.g. you are related to them via both your father AND your mother). These double (or more) connections are quite common in small isolated rural communities ... and there are lots of them in Cork, Kerry & Donegal. That's how I lost my hair.

I put everything into a private, unsearchable family tree on Ancestry (you don't need a subscription for this). In that way you can maintain your privacy and you don't have to worry about other people being able to see what you are doing. You can also be as experimental as you like without having to worry about other people copying any mistakes into their family trees. Copy across potential relatives and ancestors from the trees of your matches and any other trees you find on Ancestry (or elsewhere). There are lots of tutorials online about how to build these "mirror trees" (google them).

4. Trace trees forward in time to identify candidates for your biological parent

Having identified the “most likely” common ancestral couple, trace all their descendants down to the present day (using other people's family trees, available records, and asking your matches). If your estimations are correct, one of these descendants will be your biological father or your biological mother … but which one?

There are several tricks you can use to identify the most likely candidate for your biological parent:

a. If you have already identified your mother, then you know you are looking for your father and therefore you only need to identify family lines that have males of the right age to be your father

b. Look at locations. If you know where your conception is likely to have occurred, then there may be only one person from the list of descendants who was in “the right place at the right time” 

c. Your ethnic makeup may give clues to the likely person (e.g. his or her mother may have been from a distinctive ethnic group, and this may be reflected in your ethnic makeup results) 

d. There may also be clues from your Y-DNA or mitochondrial DNA results, and from the amount of X-DNA shared (which requires understanding the technicalities of DNA transmission) 

e. Identify your grandparents. If there are several candidates for (say) your grandfather, research their wives' family trees and see if they connect with a surname in one of the other clusters that you identified initially. 

5. Approach potential candidates for information

Armed with your theory, supported by the evidence, you decide to approach your potential close biological family (maybe a potential half-sibling). This is when the emotional rollercoaster really takes off. You can imagine how delicate this last step can be. You may benefit greatly from using an intermediary, particularly someone with professional training in reconnecting adoptees with their birth families. You usually only get one shot at this. 

If you have a social worker, you may wish them to make contact on your behalf ...  or use some other form of intermediary. It is often very helpful to have someone act as a buffer between you and your biological family. Or you may wish to contact them yourself (e.g. via the Ancestry messaging system, or via Facebook messenger, or simply sending them a letter). There is no right way to do this and you have a choice of various options, each with their pros and cons. Trust your gut feel when you get to this stage.

Initially you do not ask them to do a DNA test. You introduce yourself, tell them your story, and ask them if it rings a bell - is there a story within the family of a child being given up for adoption? You could consider mentioning the surname of your known biological mother and ask if anyone was romantically involved with someone by that name? And you could also discuss the DNA evidence that led you to their door. If you are lucky, one of the family might suggest: "would it help if I did a DNA test?" ... in which case you could say: yes, that would be great if you could.

6. Take time to enjoy your new family. 

Make time to get to know them. Develop a concrete plan for a long term relationship with them. Don’t let it slide. This takes work.


That in a nutshell is the process I use. Others will have slightly different approaches or may have other hints and tips that may speed up the process.Once you have identified one biological parent, you can start on the search for the other. I would often recommend waiting for at least one year before undertaking this second journey. 

There are a few things I have learnt through this work: the family trees on Ancestry are indispensible; so too is the ability to build trees from scratch using the records on Ancestry; first cousins are more reticent to get involved (they are too close to the supposed half-siblings in question) so it may be necessary for the adoptee to go directly to their half-siblings and “come clean”; expect surprises – they happen often, and can be emotionally overwhelming; the circumstances of the conception can be different to that expected; all adoptions are traumatic – it is never easy for a parent to give up her child; sometimes the family concerned refuses contact; sometimes the family concerned can be more helpful and more welcoming than expected.

All in all, this work is often very gratifying for all concerned and a wonderful application of genetic genealogy.

Maurice Gleeson

Sep 2014 
Updated Mar 2018

Updated Sep 2023