Figuring out how your DNA matches are related to you can be a little bit daunting and it actually
involves a lot of math. But you don't have to do the math necessarily. A lot of that math
has been done for you. Howdy, I'm Andy Lee with Family History Fanatics and today we're going to
talk about the Relationship Probabilities tool on GEDmatch. If you've been doing genetic genealogy
for any amount of time, you know that you get half of your DNA from your parents, approximately
a quarter from each one of your grandparents, and so on. As you go up through your ancestors,
all of that ends up adding into probabilities of how you might be related to other people based on
the amount of shared DNA. On GEDmatch, this tool is found on the Tier 1. You have to be a Tier 1
member and it is in the One-to-Many full version.. First, we need to enter a kit number I'm going to
enter one of mine and we have the results here. Now I've slid over to show where this is. So,
what I am looking at is. I'm looking under the autosomal column you have three columns- the
total cm, the largest cm, and the generations. The probability tool is in the total cM column.
You can see that each one of these is linked and that will open up the probabilities. When
I click on one of them, I'm going to have this probability list. And it's going to go through
and tell me what the probability is of this person being different relationships. So, for instance,
you can see this one had 1763 total shared cM, which is one of the quarter relationships
and that includes half-siblings, aunts, uncles, nieces and nephews, grandparent/grandchild,
and great-grandparent/great-grandchild in a small little bit. Additionally, this is actually divided
up into the maternal and the paternal side. So you can see that when it's looking at a half-sibling.
Well, it's more likely to be on the maternal side than on the paternal side as far as aunt/uncle.
It's almost even as far as the maternal or paternal half aunt and uncle and grandparent. It
again. There's a little bit of a difference between the maternal and the paternal side.
Overall though, you'll notice that the difference between the low one here, 12.7%, and the high,
19.1%, is not that great. In other words, there's pretty equal chance it could be any one of these
based simply on the amount of shared DNA. So, what the idea behind this tool is is to give you a clue
of where to start your search. In other words, start with the highest probability. And as you can
eliminate those, then you can start looking at the others. Lets, go and take a look at some ones that
are not as much DNA. So, here's what match shares 400 centimorgans I click on that and you'll notice
that there's actually a lot more groups here. Now when it talks about a group for instance a
first cousin once removed group it's talking about that amount of shared DNA the only relationship in
that group is a first cousin once removed if we go down to this next group a half-first cousin group
you may be thinking. Okay, so, I should be looking at just half-first cousins
well no you should be looking at half-first cousins but you should also be looking at
half-grand aunts grand uncles grand nieces grand nephews they share that same amount of DNA
as that half-first cousin if we go to the second cousin group it's not just second cousins
but it's also first cousins twice removed it's also half-first cousins once removed.
So, the half-first cousin group does not contain that half-first cousin once removed
it contains that second cousin group. Now there's been different people that have named these groups
in different ways. Some have just used letters the group A, B, C, D, E ,F, G. Others have used some
nomenclature like this. Because of the multiple different relationships, it's kind of hard to
have just a name that everybody can agree on and it's not always intuitive. For instance let's,
just take a look at this second cousin once removed group. We have second cousin once removed,
half-second cousins, half-first cousin twice removed, and first cousin three times removed.
Those all share the same amount of DNA as the second cousin once removed group.
Again, when we look at probabilities we can see that they vary in this case. It's always listed
from the most down to the least in these groups 35.5%. Little over a third is the probability that
this is a first cousin once removed. Being in the second cousin once removed group it's only a 1.8%
probability. So, it is much more likely that it is one of these first three groups than it is
one of these other lower groups. Now, this data has been compiled by
a man named Brit Nicholson. You can click on the link and read about his methodology
in this blog post here. Some of the graphs may look somewhat similar because of how the data was
created. So, if you have looked at Ancestry and they've shown you some relationship prediction,
they might have some of these graphs in their white paper. Likewise the Shared cM Tool has
some relationship prediction and it uses similar although different data sets. And so, one of the
things in comparing Ancestry, and Shared cM Tool, and this Relationship Probabilities on GEDmatch.
They're going to be slightly different and that's just because they've used different data sets.
Why? They don't just all use the same data set. It is because it's actually good to have some
different algorithms to be able to compare. One of the things you see between the three of them, if
you put in the same amount of shared centimorgans, it's going to come up with the same groups just
the probabilities are going to be off by maybe a percent or two between different things. But this
is a great tool whenever you're wondering, "Okay, how is this match related to me?"
So, I have this match here. I have no idea who they are where they're from on my family
tree. Well, the first thing I can do is click on this and be given this task of where all these
different relationships may be. The smaller amount of DNA that you share, the more groups
you're going to end up having. In this case with a 400 cMs there was what six groups. And really
only three of them were major groups. Well now, I clicked on one that is 50 cMs and you can see that
there are 10 groups. And actually all of them are somewhat evenly matched in percentages. There's
obviously these topmost groups are more by about three times than the bottom most groups. But it's
not going from 30 to these bottom groups being 0.2% or 1%. And this is one of the reasons why
when you just have a single match that you don't know. That say is 30 or 40 centimorgans you can't
really tell how they're related to you just from that amount of centimorgans because look at all
these different relationships. They could possibly be a third cousin, but really a second cousin
because there's some second cousins that are part of this group all the way down to seventh cousins.
So, there's five generations of difference between that that is possible. So, again that tool is
only available to Tier 1 members on GEDmatch, but it is embedded into the One-to-Many tool.
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