Dark matter is one of the biggest mysteries
of astronomy today.
There’s tons of evidence that it’s there,
but try as we might we haven’t been able
to find it.
In biology there’s a similar problem: dark
DNA.
When scientists were exploring the sequenced
genomes of certain birds and rodents they
noticed something odd.
A sequenced genome means everything is laid
bare, and yet certain DNA sequences were missing,
which was weird because these DNA sequences
were very important.
They controlled the production of leptin in
the birds or the secretion of insulin in the
rodents, genes that the scientists knew had
to be there, otherwise they’d have some
mighty obese birds and dead rodents on their
hands.
What’s more, the scientists studying the
rodents found the products of the missing
DNA sequences in their cells, so they deduced
that the genes weren’t missing, but were
somehow hidden.
They dubbed these elusive sequences “dark
DNA.”
Sounds spooky, but the reality is this dark
DNA may be more of a blind spot in our DNA
sequencing technology than anything else.
A closer look at the rodent’s genome found
a heavily mutated section with abnormally
high amounts of guanine and cytosine, two
of DNA’s four base molecules, called G and
C for short.
It turns out GC rich sequences are difficult
to detect, so the researchers missed this
mutated pocket of DNA at first.
This dark DNA raises questions about how quickly
mutations occur, and what genes we may have
missed when we sequenced other genomes like
our own
Which is crazy to think that there could be
more DNA in us than we realized, especially
when you consider that we only know what about
1 to 2% of the stuff we have found does.
Those sections code proteins that have some
function.
The other 98%-ish doesn’t make anything
and so we don’t know why it’s there.
This vast amount of genetic code has also
been referred to as DNA’s “dark matter.”
Apparently biologists love the dark matter
analogy, only the kind we’re talking about
now is the opposite of the first example.
Instead of knowing what a gene does but not
finding it, we’ve found a lot of genes but
have no idea what they do.
Slowly though we’re chipping away at that
riddle too.
It appears that a lot of this non-coding DNA
is still helpful for regulating gene expression,
making sure the right cells have the right
hardware, like hemoglobin in blood cell precursors
and ion channels in neurons.
Some of these sequences are almost identical
across different species like humans, mice
and chickens.
Considering we’ve been evolving separately
for up to 200 million years, researchers concluded
that these sequences must somehow be vital
to our survival.
When researchers deleted four of these genes
in mice, they found abnormalities in the mice’s
brains, and wondered if mutations in these
overlooked non-coding sections of DNA could
be responsible for brain diseases like alzheimer’s.
So there is a lot of DNA to parse through
and there could be even more we just haven’t
found because of limitations in our sequencing
techniques.
Our genome is still a pretty dark and mysterious
place, and more research is needed.
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Researchers believe that the rodents’ hot
spots of DNA mutation could be evidence of
an undiscovered and rapid mechanism of evolution.
There are known cases of rapid evolution.
To learn more about ways species can shift
in years instead of millenia, check out Trace’s
video here.
That’s it for now, I’ll see you next time
on Seeker.
