How does genetic genealogy work?

How goes genetic genealogy work?

When researching our genealogy we turn to all the available sources to mine for information and build our family trees. Following the clues we find in the documents we work out who we are related to, and how we are related to them. Genetic genealogy follows the same principle, but it uses our DNA as the key source.

When undertaking genetic genealogy we take a DNA test. Our DNA results are then typically presented to us in the form of an admixture report (our ethnicity percentages) and a list of our DNA matches.

For each of our DNA matches the testing companies usually provide us with information that can help us to work out how we are related to our DNA matches. The information can include such details as: the number of centiMorgans that we share with our match, likewise the number of segments of DNA that we share. It can also include a rough idea of the way in which we may be related (eg possible relationships). Lastly it can provide us with details of our shared matches (ie matches that we and our DNA match have in common with one another).

Genetic genealogy also provides capacity for traditional family history to be used in conjunction with the DNA evidence in order to further our research. See below.

Why should we 'follow the DNA'?

But first, let's think about 'following the DNA' and why it's a must when doing genetic genealogy. 

While our ethnicity percentages can and will continue to evolve over time, the number of centiMorgans and segments of DNA that we share with a match will not. These are fixed factual details upon which we can base our research. When doing DNA we do need to have prepared for unforeseen findings. These may include the discovery of relations that we had not previously known about; they may also include surprises to the construct of our own family tree. Relations we had thought established may be disproved by the DNA. While this can certainly be unsettling and even upsetting, if we are conducting genetic genealogy we need to use the DNA evidence as the core facts upon which we build our research - so we need to follow the DNA even if it is contrary to previous assumptions we may have held about our family tree.

Why is our traditional family history still useful for DNA research?

As you can see from the explanations above, our DNA match lists alone give us some data: details upon which we can determine possible likely ways in which we are related to our DNA matches. However, to be able to establish exactly how we are related to a DNA match we need to use the DNA in conjunction with traditional family history research.

The DNA testing companies understand this and provide tools to help us do so. When looking at your DNA match list, try out the filters to search for family names that you and your DNA matches may have in common. Likewise look for places in common. If your DNA matches have a family tree attached to their DNA test results, or available online, then explore their family tree and see whether you can spot ancestral names that are familiar to you.

While your DNA match list information may let you ascertain that you and a match are likely to be a second cousin, for instance, it is by using your traditional family history 'papertrail' research too that you will be able to establish via which ancestors you are connected - ie which pair of great-grandparents you have in common. In fact, it is by utilising your papertrail research that you will be able to establish whether you are actually a second cousin, rather than a first cousin once removed or a second cousin once removed. 

What's the difference between genetic genealogy and investigative genetic genealogy?

Investigative Genetic Genealogy (IGG) is something different to genetic genealogy. While many of the same research techniques are used (analysing the number of shared centiMorgans with DNA matches, studying their family trees, and building out their family trees in order to establish connections, they have different intentions.

Genetic genealogy is undertaken by or for family historians, to help people to trace their family trees and solve their family history mysteries. Investigative Genetic Genealogy (IGG) on the other hand is undertaken for the purpose of aiding law enforcement, usually in cases of serious crime when other means of investigation have not been fruitful. IGG is only legal in a few countries worldwide.

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