You've probably heard about your segments that you share with other people. And you might be
wondering. Well, do I have segments everywhere? in fact, do I have segments on all of my chromosomes?
Well, I'm going to answer that for one specific chromosome today. Howdy, welcome to Family History
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about DNA. During a recent conference, I got the question about the Y chromosome
and whether or not there are segments on the Y chromosome. As with most things that involve DNA,
the answer is no and yes. It's amazing that there. We can use these same two answers for a
lot of the questions. because for generally, when we're thinking about some concepts. One of these
is the right answer. but when we start to dig a little bit deeper, we find that. Well, there's
the other side of that too. Now, for those of you who are just getting into genetic genealogy,
remember the Y chromosome is passed on from father to son. It's never passed on to daughters. And
since we only ever have one Y chromosome in males, there's not another chromosome for it to recombine
with. Segments are made through recombination. And so, you would not expect any segments on
the Y chromosome. And that's why I say no. But it turns out that both the X and the Y
chromosomes have these tiny regions on either end called pseudoautosomal regions. And these regions
actually have the capability of recombining. In other words, in men, when they're passing
on their genes, the Y and the X chromosome line up together. And sometimes, those pseudoautosomal
regions will swap places. They'll recombine. Now, you might be wondering can I see this ever? And
really, the answer is no. And that's just because these are such small segments. So, to give you an
idea. The one-end pair. One the pseudoautosomal region one is only 2.6 million bases long. Now,
that may sound like a lot. But we know that on average, in the human genome, a centimorgan is
about one million bases. It's not constant throughout it but just as a rough estimate.
That's a good starting point. So, this segment that on the Y chromosome is only really about 2.6
centimorgans in length. And that means that it's not going to show up pretty much in any analysis.
because almost every analysis uses at least 7 centimorgans.
And maybe you can go down as small as 3 centimorgans on some things with GEDmatch.
but for the most part, you're never going to be able to see this. Now, interestingly enough, there
actually are about 16 genes within this small little segment. Now, the second pseudoautosomal
region is even smaller. It's only about 300,000 base pairs long and has about three genes on it.
And these are on either end of the Y chromosome and the X chromosome. So, no,
your y-DNA is never going to have segments. And that's because the pseudoautosomal regions,
while they may recombine, they are just too short to be seen on any kind of chromosome browser.
That may be why none of the chromosome browsers even show a representation for the Y chromosome.
I went through the X chromosome on a lot of them. Now, if you think about this. I should be able to
see a difference between my daughters and my X chromosome that might show these pseudoautosomal
regions if they were visible. In all the different combinations that I tried, with all the different
father-daughter pairs that I have access to. Not once was I actually able to see a distinguishable
autosomal pseudoautosomal region on the ends of these chromosomes. So, when we think about this,
males pass on their Y chromosome to their sons, and they pass on their X chromosome
to their daughters. but that X chromosome and that Y chromosome is not always going to be
an exact copy because of these pseudoautosomal regions. It's going to be 95 percent
to 99 the same. except sometimes, it's going to be different. So, for instance, there's
four different ways that you could have your X or your Y that's passed on from your father. You
could have these pseudoautosomal regions both be from the Y chromosome that your father had.
You could have one from the Y and one from the X chromosome, depending on which sides. Or you
could have both of them be from the X chromosome. So, that means 25% of the time, if you are male,
then your Y chromosome is exactly identical to your father's. but the other 75% of the time,
if you look at those pseudoautosomal regions, you will have gotten one of those pseudoautosomal
regions from the X chromosome and possibly both of them from the X chromosome that your father had.
And likewise, the flip case for your daughters. If they look at their X chromosome that they got from
their father, it will only be exactly identical 25 percent of the time. The other 75 of the time,
there will be discrepancies with those pseudoautosomal regions. but again, you can't
actually see this in any of the chromosome browsers. because these regions are just
too small. If you still have questions about DNA consider, joining our free DNA live streams. Or
become an FHFXtra member, which gives you access to even more live streams and webinars. So, I know
that was a quick answer to the question. And it probably has nothing to do with genetic genealogy
because it's a segment that you can't see. but yeah, your Y chromosome could have segments.
But we're never actually going to be able to see them with any kind of chromosome browser.
So, don't necessarily go looking for them. Now, if you would like to learn about how
x-DNA is passed down, why don't you look at this video right here. And if you want to learn
something else about DNA, then check out this video down below. Our free guide. Start again.