Epigenetics
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The Great Nature vs. Nurture Debate
 Humans
have long engaged in a debate of nature versus nurture. Are you
the person you are because you were born that way or because of
the world in which you've been brought up? If one identical twin
grows up in the city slums and the other grows up in the king's
palace, it’s likely they will develop into rather different
people, no matter how similar their genes are.
The field of
epigenetics
adds new fuel to
this issue by shedding light on how environment, nutrition and
social conditions affect how genes are expressed.
Was the twin in the palace raised by an abusive
stepmother? Did the twin in the slums have to breathe a house
full of pipe smoke? Did one eat gruel while the other feasted on
fatty desserts? These factors can cause epigenetic changes that
alter how each twin's genes are expressed. A difference in diet
could put one twin at risk for cancer and leave the other in the
clear. |
The study of Epigenetics is rewriting the
rules of disease, heredity and identity. Epigenetics refers to
reversible, heritable changes in gene regulation that occur
without a change in DNA sequence. |
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Your Body’s Video Game Settings
 Your
central programming for your inner computer is something you
inherited from your parents. They also passed on to you some of
the actual game settings they used. Think of a video game… It
offers various realism settings that allow gamers to choose just
how "real" their gaming experience will be. The default settings
may fall somewhere between pure simulator and arcade shoot-'em-up,
but the game has the potential to be more realistic, depending
on whether you turn on the appropriate options. Ultimately, you
choose whether to switch the functions off or on.
Our genes work in a very similar way. Our
accumulated genetic material, or
genome,
that we get from our parents, serves as our basic computer
program. Our gaming experience is our
phenotype,
or observable characteristics. In turn, a host of factors causes
the epigenetic processes that switch different genes on or off.
Scientists first coined the term "epigenetic" in the 1940’s as a
way of classifying changes that occurred between genome and
phenotype. |
Previously, we believed that genes predetermined
outcomes. Now, we are learning that everything we do, breathe,
smoke or eat, can affect our gene expression and that of future
generations. Epigenetics introduces the concept of free will
into our idea of genetics.
Scientists are still coming to understand the
many ways that Epigenetic changes unfold at the biochemical
level. One form of Epigenetic change physically blocks access to
the genes by altering what is called the histone code. The DNA
in every cell is tightly wound around proteins known as histones
and must be unwound to be transcribed. Alterations to this
packaging causes certain genes to be more or less available to
the cell’s chemical machinery and so determine whether those
genes are expressed or silenced.
Another well-understood form of Epigenetics
signaling, called DNA methylation, involves the addition of a
methyl group (a carbon atom plus three hydrogen atoms) to
particular bases in the DNA sequence. This interferes with the
chemical signals that would put the gene into action and thus
effectively silence the gene. |
Despite their
appearances, these two mice are genetically identical. |
Epigenetics
With no more than a change in diet, the yellow
agouti mouse was prompted to give birth to her brown offspring
that differed markedly in appearance and disease susceptibility.
Maternal methyl donor supplementation shifts the coat color of
the offspring from yellow to brown, and reduces the incidence of
obesity, diabetes and cancer. Supplementing the maternal diet
with genistein, folic acid and other compounds induced
alterations in DNA methylation that were reflected in coat color
changes in the offspring.
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About 500,000 people die from cancer each year. The cause of most kinds
of cancer is unknown. Scientists think some kinds of cancer can run in
families. Other kinds of cancer are caused by what we eat and the way we
live.
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Research shows that shortages or excesses of
food during a person’s childhood can cause epigenetic changes
that lead to diabetes, obesity and early puberty. Adaptations
that made sense during a time of famine can transfer to children
and grandchildren who live in a time of plenty. Genes become
epigenetically set to deal with adverse conditions and then
passed on to offspring who enjoy comfier conditions. Experiments
have also shown how foods can cause epigenetic changes in the
womb. Scientists have influenced coat color and deterred obesity
in mice by feeding the mother a soy-rich diet, which alters
methylation. |
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