Epigenetics: Nature vs. Nurture

Epigenetics: Nature vs. Nurture


Have you ever wondered why you are the
way you are? Are you “you” because of your genes? Because of how you were raised or could it be both? Welcome back to BOGObiology and for this screencast we’re
going to discuss the concept of epigenetics and how it helps us to
understand the interactions of nature and nurture in development. Traditionally,
we’ve said that acquired traits are not inherited, and this is true most of the
time. For instance, this creature has yellow fur. It can choose to dye its fur
neon pink, but it’s still going to produce yellow offspring. However, as we
learn more about genetics, we’ve come to realize that experiences actually can
change gene expression. Factors such as diet, drug use, and chemical exposure can
have a profound impact on our bodies. All three of these factors are capable of
changing which genes are active and which genes are inactive. We used to
believe that these changes in gene activation could not be passed on to
offspring. However, we’re recently discovering that these changes actually
are heritable and can be passed on to children, grandchildren, and sometimes
even great-grandchildren. Their genetic code itself has not been modified, but we
have slightly changed which sections are active and which sections are inactive.
These are heritable changes in gene expression that do not arise from
changes to the DNA sequence itself. This is what we call epigenetics. Another way
to think about this is that we’ve changed the organism’s phenotype without
changing its genotype. Understanding gene expression is crucial to understanding
epigenetics, so here’s a quick review. To begin with, every cell in the body
contains the exact same DNA code. DNA acts like a blueprint for making every
kind of protein that the body needs. The DNA is coiled up tightly inside the
nucleus of the cell. A gene is a section of DNA that codes for a particular set
of characteristics. Each cell type requires different traits, and thus they
need to make different proteins. The cell uses one DNA code to make many proteins
by utilizing different sections for different purposes. One cell type might
use a certain section of the DNA molecule, and another type might use a
different section. If the gene is in use and coding for proteins, we say that it
is either “turned on” or “expressed”. So, how exactly does epigenetic
influence gene expression? There are actually a number of mechanisms, but the
two about which we know the most are DNA methylation and histone modification.
Remember that the interior of the DNA molecule is made up of four nitrogen
bases; adenine, thymine, guanine, and cytosine, and that these are connected
together by hydrogen bonds. Methyl groups, which look like this, can attach to the
DNA molecule. These methyl groups can attach to some of the cytosine nitrogen
bases. The methyl groups prevent RNA polymerase, a key enzyme in the
manufacturing of proteins, from effectively grabbing onto the DNA
molecule. Since this section of DNA can no longer be used to code for proteins,
we now call it a “silenced” gene. The gene has effectively been turned off.
DNA is normally wrapped very tightly around protein complexes known as
histones. It unspools a little bit at a time in order to be accessed and used,
kind of like an old-fashioned reel-to-reel film. Adding methyl or
acetyl groups to histones impacts the ease with which they unspool. As with DNA,
methylation, the addition of a methyl group, will inhibit the manufacturing of
proteins from a certain gene. This is because the methyl group attaches to the
histone and causes the DNA to coil more tightly, making it more challenging for
enzymes to gain access. Adding an acetyl group has the opposite effect. Acetyl
groups are thought to loosen the wrapped DNA, making certain genes more accessible.
The process of both methylation and acetylation of histones is actually
reversible; the addition and removal of these groups is done by enzymes and can
be repeated many times. Research has shown that exposure to toxic chemicals
or a lousy diet can cause these acetyl and methyl groups to bind in the wrong
place, and either activate or silence the wrong genes. This is especially
problematic if, for instance, the error caused a tumor suppressor gene to be
silenced. Now let’s talk about a few examples. We’ll begin by discussing
Agouti Mice. Certain mice have a mutation in a gene called the agouti gene. The
mutation makes them obese and yellow, as well as being susceptible to heart
disease and diabetes. We would expect these unhealthy mice to give birth to
unhealthy offspring, but in 2003, Waterland and Jintle showed that
it was possible to silence the agouti mutation. The female mice were fed a diet
that was rich in methyl groups. The methyl groups seemed to silence the
agouti gene, and the offspring were born healthy. Studies have also shown
correlations between human maternal health and the health of the offspring.
We encourage mothers to eat folic acid before and during their pregnancy
because it helps with proper neural tube formation. Another famous experiment
showed the effect of epigenetics on the stress response. inside of the midbrain
of a rat is a region known as the hippocampus. Within the hippocampus are
structures known as glucocorticoid receptors, which help mediate the stress
response. Receiving adequate care early in life seems to be a key factor. Baby
rats who receive adequate care and grooming from their mothers in the first
weeks of life appeared to demethylate the genes for glucocorticoid receptor
development. When we remove the methyl groups, it switches the genes on and
allows for proper development of glucocorticoid receptors within the
hippocampus. These rats generally grow up to become healthy and well-adjusted
adults. If baby rats do not receive adequate care, however, they never developed
the same level of glucocorticoid receptors. They also grew up to be highly
anxious adults who had a very difficult time managing their stress response.
There appears to be a strong relationship between maternal care and
the development of a healthy stress response later in life. Researchers are
looking into the possibility of a similar relationship in humans by
studying victims of childhood trauma. Hopefully, in years to come, we will
continue to expand our knowledge of epigenetics, how it impacts our lives, and
the extent to which epigenetic changes might be reversible. All right, that’s
pretty much it for this week. If you found this video useful, I hope you’ll
consider subscribing to my channel and also checking out some of my other
videos. I put a lot of time and effort into creating them, and I’m always
looking for new content ideas, so please leave your thoughts in the comment field
below. Thanks for watching and, as always, please don’t forget to subscribe!

9 thoughts on “Epigenetics: Nature vs. Nurture

  1. can you explain in details about the discordance in phenotypic genetic traits of monozygotic twins in relation to epigenetics. it will be quite helpful.

  2. can you explain in details about the discordance in phenotypic genetic traits of monozygotic twins in relation to epigenetics. it will be quite helpful.

  3. That was very concise! Thanks. & yes! That's a really big question in the world of Biology & Philosophy, the question of whether it's nature or nurture that forms our personality & other things!

  4. this video is awesome! I wasn't understanding my behavior science class until I watched this and now the long nature vs. nurture question makes sense!!! thanks! also your voice is so nice to listen too! great prosody!

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