Siblings can have a common match that they don't share the same amount of DNA with. Well, today's
video is the result of another user question. If you have questions, then feel free to put
them in the comments of this video or any other video, and maybe your question will turn into a
video on another day. And actually, the person who made this comment pointed out that they,
and I think their sister, matched a common person. She by 154 centimorgans and her sister by only 80
centimorgans- which is a big difference between that. So, what I want to go over today an example
of siblings, and actually a first cousin of those siblings, matching a third cousin to all of them.
And the difference just in the amount of DNA that they all share. What I'm comparing is I'm
comparing four siblings (me and my three brothers- so we all have the same parents) and a first
cousin of ours (so we are all related to this first cousin the same way). His mom is our dad's
sister. And we're going to compare these five people than to a third cousin once removed. So,
this third cousin once removed that's the same relationship to all five of us. Now,
if we go over to DNA Painter to the Shared CM Tool and we look at a third cousin once removed, we can
see some data that has been gathered from a lot of examples. On average, they share 48 centimorgans.
That's what the 48 in the middle is. But over all these different ones, there's a range between 0
and 192 centimorgans. So, that's actually a pretty big range that any third cousin, once removed,
can share. In this case, I'm looking at five close to the rated. Four of them are very closely
related because they're siblings to this third cousin once removed. And here is the quick example
of it. You can see that me, I happen to win. I share the most DNA with them- 118.8 centimorgans.
One of my brothers shares 111.3. But then, the next brother only shares 70, which is quite a bit
of a jump from the 118 - 111. But my other brother only shares 35 centimorgans (which again). Now,
we've got this big gap showing up. And my cousin, he only shares 11 centimorgans. Let's go and map
this out on the histogram. If we go and we click on that third cousin once removed on DNA Painter,
we get this histogram. This distribution of how or who shares how much with them.
And we can see that this is centered right around 50 centimorgans, which makes sense because, on
average, it's 48 centimorgans. There's quite a bit just below 50, and there's quite a bit just above
50. And then it tapers off. Well, if I plot out where me and my brothers and my cousin all are,
you can see that, hey, we actually spread over this whole range. Me and one brother,
we're at the top end of this range. And then, I have two brothers that are on either side of the
middle of the range. And then, my cousin happens to be on the tail end of the range. And remember,
we are all third cousins once removed to this match. So, it's extremely possible in fact,
it's probably likely, and in some cases, you should expect it. Whatever you're looking at,
siblings with a common match, they're probably not going to share close to the same amount of
DNA. In many cases, that I might share widely varying DNA. Now, me and my three brothers,
we all share more than my cousin. Probably, and I don't know for sure, because I haven't had his mom
tested. But probably, because my dad shares much larger segments with this match than his mom does.
And so, he didn't have the opportunity to even get near as much as we did. But even among the four
siblings, we range from 119 all the way down to 35 for this same match. What this can also do is,
when you have siblings that have all tested, it is actually great to use all of them to compare
to unknown matches. Because then, you have a comparison on a chart like this that can
help eliminate some different relationships. It's the same thing as using the WATO Tool to
see where you might be related. Because you, all four of your siblings, all four of you have the
same relationship with this unknown match, which means that range whatever you all share has to
fit into the range of whatever that relationship is. So, in this case, a third cousin once removed.
We all fit in that 0 to 192 range. If this was an unknown match, then we would be able to say
confidently that it could be a third cousin once removed because we all fit within that range. If,
for instance, I happen to share, let's say, 220 centimorgans with them, then we could say this
is probably not a third cousin once removed because one of those is outside of the range
of that relationship. So, if you have siblings who haven't had their DNA tested, then I would
encourage you to go and get them DNA tested because there's many things that you can do with
siblings as far as comparisons that you're not going to be able to do with just yourself. Now,
if you'd like to learn more about how to use the Shared CM Tool, then watch this video up top here.