Kind: captions
Language: en
[Applause]
inside each one of your cells there is
six feet of DNA made up of six billion
letters of genetic code now your DNA is
split into 46 pieces each 3 to 4 cm long
called chromosomes now normally we think
of chromosomes as looking like this but
they only take that form when a cell is
ready to divide so usually DNA is just a
wiggly thread within the nucleus now if
you can imagine DNA is only about 2
nanom wide but a chromosome is cm long
so you would think that it would get
tangled worse than the headphones in
your bag so the DNA is actually wrapped
around proteins called histones now
those histones have Wiggly Tails which
will come in handy as we'll see in a
moment your unique set of DNA first
formed when 23 chromosomes from your mom
mixed with 23 from your dad now 22 of
those chromosomes from each parent form
matching pairs but the 23rd set is the
sex chromosomes so two X chromosomes
make you female and an X and A Y make
you male now since the male sex
chromosomes are different both can
remain active for the rest of your life
but for females one of the X chromosomes
needs to be inactivated in order for
proper development to occur this happens
when a female embryo is Just 4 days old
and consists of only 100 cells right now
in this cell the ex chromosome from Dad
and the one from Mom are both active but
through a tiny molecular battle one of
the X chromosomes wins and remains
active while the other is
inactivated this is done by packing the
DNA closer together and making
modifications to those dangly histone
tails that signal this inactivation new
structural proteins are also added to
bind everything closer together and
finally methyl groups these tiny little
molecular markers are added to the DNA
to basically signal to the cell that
this DNA shouldn't be red so all of this
together makes the DNA very difficult to
access for the molecular Machinery that
would harness the code in this DNA it is
Switched Off This DNA is silenced in
contrast the active X chromosome DNA is
more spread
out this allows better access to the
genes on the
chromosome histones can be slid along
the
DNA or removed entirely
and the histone Tails have a different
modification signaling this DNA is
active now all of this makes it possible
for RNA polymerase to access and
transcribe this DNA into messenger RNA
which then goes out into the cell and is
used to make a protein now what's
surprising about X chromosome in
activation is that it seems kind of
random which X chromosome wins I mean in
some cells dad's ex chromosome winds and
in others mom's ex chromosome winds so
this 100 cell embryo ends up with a
mixture of active X chromosomes but from
this point forward as these cells divide
they maintain the active X chromosome
that they had inside so all of the cells
with dad's active X chromosome give rise
to further cells with dad's active X
chromosome and this continues on into
adulthood so if you could look at a
woman's skin and see which X chromosome
has been inactivated you would see a
stripy pattern which shows the growth
and Mig
of all of these first 100 cells when the
embryo was just 4 days
[Music]
old now of course you can actually see
that in humans but you can see this with
Calico cats and that's because the gene
for coat color is actually on the X
chromosome so just by looking at the
pattern of her spots here her dark and
light spots you can see where her mom or
dad's ex chromosome has been inactivated
and this also shows us that only female
cats can be calico cats and that's
because well only female cats can
inherit two X chromosomes with two
different color
genes now this is just one really cool
example of epigenetics but epigenetics
doesn't normally work on one whole
chromosome in fact it's at play in all
of your chromosomes turning on and off
your genes for example it's epigenetics
which makes a pancreatic cell capable of
producing insulin because that Gene is
switched on there but Switched Off
everywhere else what's more interesting
is that it seems the behaviors you take
can actually affect your epigenetics and
even weirder perhaps the things that
your parents or grandparents did can
affect your epigenetics now can affect
your DNA so you are not just a product
of your genetic code you're not just a
product of your DNA you are also a
product of your epigenetics and that is
influenced by your behavior and the
behavior of your ancestors
[Music]