I know that we've answered this in some ways in other videos, but the way that this was asked
made it seem like, well, maybe I need to be a little bit more comprehensive about this. So,
howdy! I'm Andy Lee with Family History Fanatics, and today we have a user question:
if we all share almost 100% of our DNA, how is it possible to tell apart each person through DNA?
And that's an excellent question because when you think about it, if
we are practically 100% the same, how do we tell what's different?
Now, if you think about going out and let's say you go to a train station and you see a bunch
of people, you are easily going to be able to distinguish some of them based just on their hair
color, their skin color, maybe what clothes they're wearing, perhaps how tall they are,
or any number of other things that you can just see all these differences. But DNA is not looking
at those outward differences necessarily so much. We are looking at the code that codes for those
outward differences, but intermingled in that code is a bunch of information that is all the same.
According to the National Human Genome Research Institute, humans—all humans, every single human
that's ever lived or ever will live and currently lives—share 99.9 percent of their DNA. In other
words, 99.9% of me and you and anyone else is the exact same. And it has to be this way because
if it wasn't, more than likely you wouldn't be able to live or at least you wouldn't be human
anymore because it's really that 99.9 percent that makes us human. And it's this point one
percent difference that just gives us different hair color and other little traits like that.
This point one percent, this includes insertions, which is when there is an extra letter put into
the DNA; it's deletions, that's when a letter is taken out of the DNA; and it is substitutions,
that's when a letter is changed. Now, you might have heard of these things all called SNPs
(single nucleotide polymorphisms). These are the differences that we have with others.
Since we are 99.9 percent exactly the same with everybody, there is point one percent that we
could be different. Now, you'll see in a second it doesn't necessarily mean that we are different,
but we could be different. There are three billion locations in our genome, so 0.1 percent
times three billion is three million. Think about 3 million places that we could be different. Now,
this, like I said, might be our hair color; it might be our eye color; it could be our skin tone;
it could be our height; it could be our blood type; it could be three million different things.
And really, those three million different things affect lots of things, so there's probably more
than just three million, but think of it as three million different ways we could be different.
Now, how could we be different? Well, each SNP has two letters, and you can really have three
possibilities between those. You could have both of them the same letter of one type,
both of them the same letter of another type, and that represents the PP and the QQ, or you could
have one of each letter, a P and a Q. So, there are three different ways that each one of these
differences could be different. Let's take a look at two SNPs and see how many varieties we have.
So here are the three different varieties, and now if the first SNP was PP, your second SNP
could be PP, it could be QQ, or it could be a PQ. Alright, there are three different possibilities.
But if your first SNP was QQ, then it could be PP,
Q, or PQ for your second SNP. That's another three possibilities. And if you were a PQ,
your second SNP still could be PP, Q, or PQ. Each SNP is independent of all the other SNPs,
and so you see with just looking at two SNPs, there are nine different possibilities
that we could have, nine differences, nine distinct individuals just with two SNPs.
And we already said that there were three million SNPs. Now, I know going back to math,
this number may look odd and you may not like it, and even mathematicians and astrophysicists,
whatever, are going to look at this and say, "That's a really big number."
Three to the three million because there's three ways you can be different within a SNP, and
there's three million SNPs that could be different between people. So, three to the three million,
this is like a ten followed by 1.4 million zeros. It is a huge number. It's such a big number you're
not going to be able to calculate it out. Every online calculator basically says this is infinity.
In fact, it's infinity long before it ever gets to this. This is a huge, massive, enormous number.
But the good thing is that companies, they only look at 500,000 SNPs. That means we can change
that to three to the 500,000 power, which is like 10 followed by 240,000 zeros. It's still,
guess what, a huge number. It's bigger than anything that we actually do things with. Now,
we can actually cut this number down even more because if you take any random person, you share
about half to three-quarters of those SNPs with them. Obviously, if you're more closely related,
you're probably closer to that three-quarters, but any just random person that you grab off
the street, you and that person share at least probably half of all of those SNPs.
So let's take that number and let's cut it down to three to the 150,000. And guess what? We're still
in large number territory that you just can't calculate. You can't use it in any computer
because there's not enough spaces to do the calculations with it. It is that large of a number
still. And that is the key to being able to tell different people apart. Even though we are 99.9%
similar, which is almost as similar as you can get, even though that is the case, there's still
an innumerable possible ways that we are different genetically. And that is just in looking at the
500,000 SNPs that these companies are looking at. And so, it's really easy, actually, to tell
people apart. In fact, the only people that these genetic tests would not be able to tell apart is
identical twins. Now, even then, identical twins aren't actually fully identical. Every person has
its estimated anywhere between five to a hundred unique mutations in their DNA that they are born
with, and that includes identical twins. So most of those mutations, if not all those mutations,
are not SNPs that are tested for, which is why identical twins show up as being the same
person when we do a genetic test. But everybody else, genetic tests can easily tell them apart.
Now, if you like this video, then you can watch this other one right
up here. Be sure to like and subscribe to our channel, and we'll catch you next week.