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Epigenetics: Triggers That Switch Genes On and Off
Recall that genes can be either active (expressed, as the hot water activates a tea bag)
or inactive. Epigenetics studies the molecular mechanisms by which environments
can trigger or block genetic expression. Genes are self-
Genes
Figure 1.1-3 regulating. Rather than acting as blueprints that lead to
Epigenetic expression the same result no matter what the context, genes react.
Beginning in the womb, life An African butterfly that is green in summer turns brown
experiences lay down epigenetic in fall, thanks to a temperature-controlled genetic switch.
marks — often organic methyl The same genes that produce green in one situation pro-
molecules — that can influence the
expression of any gene in the DNA duce brown in another.
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
segment they affect. (Research Prenatal Drugs, toxins, Our experiences create epigenetic marks, which are
from Champagne, 2010.) nutrition, stress
often organic methyl molecules attached to part of a DNA
strand (Figure 1.1-3). If a mark instructs the cell to ignore
Postnatal Neglect, abuse, any gene present in that DNA segment, those genes will
Copyright © Bedford, Freeman & Worth Publishers.
variations in care be “turned off” — they will prevent the DNA from pro-
ducing the proteins normally coded by that gene. As one
®
AP Science Practice geneticist explained, “Things written in pen you can’t
Juvenile Social contact,
Research environmental change. That’s DNA. But things written in pencil you can.
complexity That’s epigenetics” (Reed, 2012).
The environmental factors men-
tioned here — diet, drugs, and Environmental factors such as diet, drugs, and stress
stress — could be variables in an Adult Cognitive can affect the epigenetic molecules that regulate gene
epigenetic study. If the research challenges, expression. Mother rats normally lick their infants. In
manipulates the amount of stress exercise, nutrition experiments, infant rats deprived of this licking had more
the rats experience, it would be
the independent variable. epigenetic molecules blocking access to their brain’s
“on” switch for developing stress hormone receptors.
When stressed, animals that had above-average levels
of free-floating stress hormones displayed more stress
(Champagne et al., 2003; Champagne & Mashoodh, 2009).
Epigenetics provides a possible mechanism by which
epigenetics “above” or “in Gene expression affected
addition to” (epi) genetics; by epigenetic molecules the effects of childhood trauma, poverty, or malnutrition
the study of the molecular may last a lifetime (Neves et al., 2019). Such experiences
mechanisms by which may leave fingerprints in a person’s
environments can influence genome. Some epigenetic changes may
genetic expression (without a even get passed down to future gener-
DNA change).
ations. Holocaust survivors and former
prisoners of war have shared epigenetic
alterations with their offspring (Costa
et al., 2018; Yehuda et al., 2016). Such
findings have led some evolutionary
biologists to theorize that inheritance
Lasting effects Canadian occurs not only through gene trans-
Senator Murray Sinclair received a mission, but also through environmen-
humanitarian award from the Canadian tal influences (Uller & Laland, 2019).
Psychological Association for an
in-depth report on the devastating Evolution, they argue, shapes human
effects of Canada’s long-running culture and experience, which influence
residential school program that evolution. Other scientists dispute the
removed Indigenous children from their
families. Psychologist Susan Pinker idea that children can inherit their par-
(2015) observed that the epigenetic Adrian Wyld/The Canadian Press/AP Photo ents’ epigenetic changes (Horsthemke,
effects of forced family separation “can 2018; Ryan & Kuzawa, 2020). Stay
play out, not only in the survivors of
residential schools but in subsequent tuned: This scientific story is still being
generations.” written.

16 Unit 1 Biological Bases of Behavior

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