We're talking about YDNA, one of the concepts that comes up
is genetic distance and this can be a little bit confusing
for many people. So, if you were asked, how many
generations is a genetic distance of one equal to and in
this case, they had a genetic distance of ten and so they
were trying to figure out, okay, what is the conversion
between generations and genetic distance so that we know what
the multiplier is? It's not that easy. In fact, it would be
great if it was that easy but it's not that easy because
there's a lot of different things going on. So, let's go
take a look at our YDNA matches. Now, on Family Tree
DNA, if you have tested with the YDNA, you go down to your
YDNA results and there is your YDNA matches. So, the first
thing I want to point out with YDNA matches is your YDNA is
passed down from father to son, father to son, father to son.
One of the things that many people look for as far as
research in YDNA is that Patrilineal line and that
surname that is attached to it now I had this problem before I
actually tested YDNA where I found out that my surname Lee
is not the patrilinial surname once you get back four
generations. There was a guy who actually changed his name
to Lee basically to hide from the law and so I found out what
this patrilineal surname was before I done my YDNA test.
After I did my test you can see here are the names. Swift,
Sanders, Knuckles, they're not Lee but they're also not
Garnett. As I go further down this list, I do find some
garnets. I find some Simmons, I find some Thackers. That's like
one, two, three, four, five, six different surnames in just
11 people. So, my line apparently is not very stable.
I'm not sure if it's the Knuckles. I'm not sure if it's
the Garnett or if it's the Sanders or one of these other
ones but obviously, there was more instances such as in my
family. In my family, somebody actually changed their name. In
some of these other families, there might have been a NPE
event that that surname got changed or there might be name
changes for other reasons and that's why just in my line of
11 people, it's not that many. I've got six different surnames
represented. There's not really any consistency there but then,
when we go back to genetic distance, I can see here,
there's four steps and six steps and those are my closest
relations. So, let's go back to the homepage here and under the
see more, we want to go to why stir results to start to
understand what these genetic differences are meaning. Now,
on this page, we can see a lot of letters and numbers that are
not what we normally see when we're looking at autosomal DNA.
Autosomal DNA, we are talking about how much shared CM, how
much shared centimorgans. That absolutely nothing to do with
what you're looking at right here. Autosomal DNA shared
centimorgans is looking at snips - SNPs and stringing those
together to create a segment whereas YDNA in this case is
looking at stirs- STR that stands for short tandem
repeats. In other words, there's a set of letters that's
repeated multiple times and that is what you're seeing
here. First off, the marker indicates the place on the
genome. In other words, it could be you know, a million
spots in on the Y chromosome to get to DYS three nine three. I
don't know exactly the location of it but there's a specific
location and it tells you then how many repeats. So, this
series of letters at that location is repeated 13 times
and you can see that for each one of these different markers
that I have been tested for. Now, a genetic distance is
determined by how many differences between your
numbers and everybody else's numbers or the matches numbers
so for instance me and this match we may match everything
on these one through twelve but let's say that hey right here
on DYS 454 he has a ten and I have an eleven. Well that gives
us a genetic distance of one. And if say that oh if we also
look at DYS 576, he has 19 I have 18 well that adds another
one to it and if we go to another one DYS 590 he has a
seven I have an eight that adds another one to it and maybe on
this DIYS 511 he has a nine I have a 10 that adds another one
and now we're all the way up to a genetic distance of four
basically these numbers can change. In other words a number
of repeats can change each generation. So the genetic
distance is in an indication of how far removed you are but it
is not generation by generation in other words these mutations
which may make the numbers different don't necessarily
happen every generation but they do have to happen at a
generation and so four in this case a genetic distance of four
indicates that hey there's been four times that we've had a
mutation over the generations that might equal several
generations each one of these also mutate at different rates
and so that all has to be added into it and we can find this
tip report by going and clicking on the little bar
chart at the end of that match. So, let's go and let's take a
look at mister Sanders and I. Now, I chose mister Sanders
because this is with 12 markers and mister Sanders also matches
me with 6seven markers. So, let's look at twelve markers to
begin with. What this tip report is is it's telling me
that there's a 33% chance that me and mister Sanders are
related within four generations okay only a one out of three
chance it's telling me that there's just over a 50% chance
that we're related within eight generations and it's telling me
that at twelve generations it goes up to 70 and by 24,
generations. it's still only 91%. so it's it's not that
certain even at 24 generations, which is far beyond when we're
going to find genealogical records. Let's say your 2-four
generations is probably 600 years. So we're talking the the
14hundreds that we might have a common ancestor. Now you'll
notice at twelve markers me and Mister Sanders share or we have
a genetic distance of zero. In other words all of these first
12 we match exactly. So where the differences come in is in
later ones. So if we were just looking at 12 we would come up
with these percentages. But since we both tested at 6seven,
our genetic distance here is actually six. In other words,
there are at least six differences between me and
mister Sanders in these others. It looks like we might be
somewhat closer related with just twelve because it's a zero
but once we go to sixty-seven, there's at least six
differences. Now, you'll notice a couple of things then because
of that. First off, between one and four or between within four
generations, it go drops from 33% down to 22%, okay? So, it's
much less likely that we are related within four generations
and in fact, I know through four generations. Again, this
is just on my paternal line. I actually know all of the
descendants of that and mister Sanders is not one of them. So,
I know for sure that he's not within that which percentage
wise makes sense. At eight generations, it moved from
50percent, 55% up to 66%. So, it actually went up and that's
because as you read this, hey, each marker has a different
mutation rate. So, identical genetic distances will not
necessarily yield the same probabilities. In other words,
a genetic distance of one for this match is not the same as a
genetic distance of one for another match. To answer this
viewer's question about how many generations is the genetic
system one equal to? It's not. It is. It's not easy. It's it's
there is no correlation directly of generations to
genetic distance. There are probabilities associated with
it but those probabilities are affected by where that genetic
distance difference comes from. Which marker has that mutation
on it. But the other thing that you can see here is whereas
with twelve at twenty-four generations we're only 91%
certain that we're within that. At twenty-four generations
we're 99 point nine percent. We're basically 100% certain
that we're later within 2-four generations 99. 5 within 20.
You know 97% within sixteen and 90% within twelve. So twelve
generations is really only about 300 years. So there might
be some records that we can find to actually link us
together. Now it turns out that my line with where the name
change happens with Garnet. I haven't been able to push that
back farther than that first Garnett James Garnett who
immigrated to the United States from England in 18 18 3five,
1840 around that time frame which is only about 1 50 years
ago. So, I'm only about halfway to where me and mister Sanders
could possibly match up with but what we can see from this
is that for lower generations, particularly that four
generations, increasing in markers even though you may go
from zero genetic distance to six genetic distance changes
that percent downward whereas it actually increases that
percentage for others and that's just because of all the
the math that has to go into calculating these probabilities
it's not a simple answer and so instead of trying to get a rule
of thumb of how closely really this is I would go with a
couple of things one if it's not a genetic distance of one
or zero it's probably not worth looking at more than likely
you're talking about people that are 300 years or more
distantly related from you and there's not going to
necessarily be a paper trail for that and two, take a look
at the probabilities because one of the things that I can do
here and again, this is with a sixth generate, a sixth genetic
distance. I know, like I said, I am not related within four
generations. So, I can increase that to four generations. I can
recalculate it and now, you will see that hey, it's saying
that yeah, you could be wrong at four generations but eight
went down. In fact, all of these went down just slightly.
As I push that back farther, maybe I know that hey, it's not
within six generations. Well, it's going to continuously
recalculate those and that is one of the great things about
this this calculation is you we can put in what information we
know how back I know I'm not related to him for certain
because I know all of the relatives in that time frame
and I can see that yeah it's pushing more now towards that
twelve rather than towards that eight so I'm looking at really
the extent as far as records but again this is one that was
a genetic distance of six I don't have anything closer than
that on my list you can see that hey this four steps I got
I take that back I have one person who's four I don't have
anybody who's a genetic distance of one or zero and so
I haven't done much with YDNA simply because of the fact that
I don't have any matches close enough to do something with
YDNA. There is no conversion between number of generations
and genetic distance. Genetic distance is more of a
probability determination based on where those differences are.
Honestly, just look at your matches that are genetic
distance of one or zero and if you can be able to solve those,
then, it might be worth looking at of the others. If you like
the video, smash that like button and you can watch this
other video up here if you want to learn something more.