you've heard that you did 50% of your DNA from each parent and 25% from each
grandparent 12.5% from each great grandparent and on and on and on
but is that really true
howdy I'm Andy Lee with Family History Fanatics where we help you
understand your DNA climb your family tree and write your ancestor stories
along the way today we're talking about where we get our DNA now let's begin by
understanding what DNA we're talking about today we're just talking about
autosomal DNA now autosomal DNA is the 22 pairs of chromosomes that you have
that does not include your mitochondrial DNA and it also does not include X or Y
that's the 23rd pair of chromosomes that you have so we're just talking about the
first 22 pairs of chromosomes now since there are 22 pairs of chromosomes that
means there are 44 total chromosomes that we're concerned with today so when
it comes to our parents DNA what do we get from each one of our parents well
this is actually a really easy question to answer we get one set of chromosomes
from each parent and that means we get 22 chromosomes from each parent so in
order to do the math you just have 22 divided by 44 that equals 50% when we're
talking about autosomal DNA you always get 50% of your DNA from each
of your two biological parents simple as that
so if we get 50% of DNA from each one of our parents always do we get 25% of DNA
from each one of our grandparents because our parents had two parents as
well now that would make logical sense and if you just do the math that's
usually how it is presented but that's not always the case in fact
that's mostly not the case now you guys are all right each one of our parents
also has 22 pairs of chromosomes and each of these pairs comes from either
our grandfather their father or our grandmother their mother so in one pair
they have a grandfather chromosome and they have a grandmother chromosome now
that's talking about us it would be their mother and their father but for us
it would be a grandfather chromosome and a grandmother chromosome that our
parents have this next part is really important to understand before either
one of your parents pass on a set of chromosomes to you the chromosome in
other words the pair that they have goes through a process called recombination
during that process that pair of chromosomes one from the grandfather one
from the grandmother they may swap different locations so that the
chromosome that's passed on to you is not necessarily from the grandmother or
the grandfather but it is actually a combination of the grandmother and the
grandfather chromosomes that your parents have let me say that again each
chromosome that you have let's say for instance the chromosome number one that
you got from your father that chromosome is a mixture of the chromosome one that
your father's father your grandfather and your father's mother your
grandmother combined together into a new chromosome which is what you receive so
because of this there are several different ways that you can inherit DNA
from your grandparents and this is on an individual chromosome level and it
differs not just for each individual chromosome but also each person
let's go through the possibilities the first possibility is you get a
chromosome that is a hundred percent from your grandfather in other words
your father passes on his paternal chromosome complete to you now let me
show you what that looks like if I'm going to Jed match and I compare
myself to my paternal grandfather you can see here on chromosome number six
that it is all blue along the bottom indicating that it is a half match all
the way across in other words my chromosome number six from my father is
the exact same as the chromosome that he inherited from his grandfather that's
pretty cool likewise the same thing can happen with
your grandmother you can inherit a chromosome that your
parent received from their mother exactly the way that your parent has it
if I look at myself again and this is comparing to my grandfather
I look at chromosome number 22 and I see that it is black across the bottom that
indicates that there is no match for my grandfather which means I inherited this
chromosome from my grandmother from my paternal grandmother so it is an exact
copy of the chromosome that my father has which he received from his mother
now we also can receive a chromosome that is mostly from our grandfather what
might this look like well here is my chromosome number 11 and you can see
that the majority of it is blue indicating a half match that matches me
and my grandfather but then there is on the end a little tail portion that is
black indicating that it is not a match to my grandfather so it is a match to my
grandmother and so this chromosome chromosome number 11 is mostly from my
grandfather but some of it is from my grandmother now we can go the flip way
and you can receive chromosomes that are mostly from your grand
if I look at chromosome number seven it is black almost the entire length until
right at the very end there is a little tiny bit of blue indicating a half match
and that little half match I match with my grandfather
but this chromosome is mostly the chromosome of my grandmother and finally
you can have a chromosome that's about equally matched from both grandparents
so in other words during that recombination process it put bits of
each one together to make it about 50/50 what does that look like well here's my
chromosome number one you can see there are two segments that are blue and there
are two segments that are black the blue segments are the ones that I received
from my grandfather and the black segments are the ones that I received
from my grandmother now they're varying lengths but overall it's about 50% from
my grandfather and 50% from my grandmother one of the important things
to remember is this is a random process so you are not going to be able to
predict which one it is until you actually compare yourself with your
grandparents now if I take my full set of chromosomes and I compare it to both
my paternal grandfather and my paternal grandmother I got 25% from my paternal
grandfather and 25% from my paternal grandmother now I said at the beginning
that it's not always the case but this looks like it's perfect
I got 50% from my parents I got 25% from each one of my grandparents yeah but see
I'm sort of the exception because if I look at my brothers here you can see
that well some of them are 27% looks like down to 22% 23 24 25 26 they're all
around 25% but none of them actually got 25% from either one of our paternal
grandparents these are the same paternal grandparents and so what you to
understand is is there is actually a range of DNA that you could inherit from
your Grandpere it's just like you saw with me and my
brothers I inherited 25% from each one so I inherited equal amounts but my 3
brothers did not inherit equal amounts in fact all three of them inherited a
little bit more DNA from our grandfather than we did from our grandmother so
where is this range of DNA it's about between 20% and 30% so you
should expect to see numbers that are in this range now there's some extreme
cases that may go below this or may go above this but those are actually pretty
rare for the vast majority of people if you compare your DNA with any of your
grandparents you'll find that you share about 20 to 30% of your total DNA with
them the last important thing to remember is that if you receive 30% from
your paternal grandfather you must receive 20% from your paternal
grandmother why is that because their DNA is what makes up your father's DNA
and you receive 50% of your DNA from your father so their DNA has to add up
to 50% so 30% you get 20% if you have 25% you're gonna get 25% that is how it
works so we always receive 50% of our DNA half of our DNA from each one of our
parents but once we get to our grandparents and our great-grandparents
recombination makes it so that we don't always share
the exact average it will be around that average for our grandparents it's 25%
for a great-grandparents it's 12 and a half percent but it's not necessarily
going to be that exact amount now if you would like to learn some more about how
relationships work with DNA then check out one of these two videos right here
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