Since epigenetics can influence every
aspect of our biology by acting on our
genes, learning the rules that govern
where epigenetic markers are placed
or how these precise markers are
maintained could help us begin to an-
swer some very long-standing ques-
tions in biology. Questions like why
disease susceptibility increases with
old age, why some people live to much
older ages than others, or even po-
tentially accelerate the adaptability of
species to environmental change.
Curiously, the pattern of epigenetic
markers on the genomes of identical
twins can differ, despite their identical
genetic make-up. These differences
become more pronounced with age,
suggesting that the older identical
twins get the less identical they are.
This phenomenon called epivariation
(surprise, surprise) can be driven by
many factors such as random varia-
tion, mutation in the DNA sequence
onto which epigenetic markers are
placed or, most excitingly, environ-
mental stimuli. Now why is that excit-
ing I hear you ask?
Well, genetic variation by mutation is
a slow process that relies on the suc-
cess of subsequent generations in
the wild, something which is not likely
considering that genetic mutation oc-
curs in random locations on the ge-
nome and is therefore indifferent to
the environmental pressures placed
on an organism. Epivariation therefore
offers a far faster way for an organ-
ism to adapt to changes in its environ-
ment and potentially pass these im-
mediate benefits onto their offspring.
Transgenerational epigenetic inherit-
ance, as it is known, excites the living
shit out of me and epigeneticists alike
as it suggests that the decisions we
make about the environment in which
we live can have some influence over
the genetics of our descendants; not
the DNA sequences they inherit but
how they are used, thus blending na-
ture and nurture into one. the electric shock and then freeze in
place when the smell arrives, just clas-
sical Pavlovian conditioning. Well they
next allowed the conditioned mice (F0)
to rest for two weeks, then mate with
unconditioned mice. The offspring
(F1) were then exposed to acetophe-
none but without any foot shock. They
found that the offspring observed
similar freezing behaviour to their par-
ents, and significantly greater than the
different control groups. Proving that
it was odor specific, not a learned be-
haviour from the mice’s parents and
that it required sexual transmission
via gametes. This behaviour was even
transferable to the next generation
(F2), even though neither F1 nor F2
were ever exposed to the odor prior to
testing.
In 2014 an epigenetics study entitled
“Parental olfactory experience influ-
ences behaviour and neural structure
in subsequent generations” [3] found
that by providing an odor stimuli to
mice (acetophenone, kind of like or-
ange blossom I’m told) and then
shortly afterwards giving them a mild
electric shock they could cause the
mice to freeze in response to the odor
alone. Nothing surprising, right? The
mice learn to associate the smell with Spooky huh? Inheritance of a behav-
ioural trait across 2 generations that
needs only gametes to occur. Looking
deeper into the possible cause of this
phenomenon the researchers checked
the methylation state of the gene
which produces the specific smell-re-
ceptor for acetophenone. They found
that the gene had significantly lower
methylation than controls, indicat-
ing dis-inhibition of expression of this
gene, and therefore greater sensitivity
In twins, epigenetic markers decrease in similarity over time (Yellow = similar; red and green = dissimilar) [1]. Lower twin picture [2].
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