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  • Here's a conundrum:

  • identical twins originate from the same DNA,

  • so how can they turn out so different

  • even in traits that have a significant genetic component?

  • For instance, why might one twin get heart disease at 55,

  • while her sister runs marathons in perfect health?

  • Nature versus nurture has a lot to do with it,

  • but a deeper related answer can be found within something called epigenetics.

  • That's the study of how DNA interacts

  • with the multitude of smaller molecules found within cells,

  • which can activate and deactivate genes.

  • If you think of DNA as a recipe book,

  • those molecules are largely what determine what gets cooked when.

  • They aren't making any conscious choices themselves,

  • rather their presence and concentration within cells makes the difference.

  • So how does that work?

  • Genes in DNA are expressed when they're read and transcribed into RNA,

  • which is translated into proteins by structures called ribosomes.

  • And proteins are much of what determines a cell's characteristics and function.

  • Epigenetic changes can boost or interfere with the transcription of specific genes.

  • The most common way interference happens is that DNA,

  • or the proteins it's wrapped around,

  • gets labeled with small chemical tags.

  • The set of all of the chemical tags that are attached to the genome

  • of a given cell

  • is called the epigenome.

  • Some of these, like a methyl group, inhibit gene expression

  • by derailing the cellular transcription machinery

  • or causing the DNA to coil more tightly,

  • making it inaccessible.

  • The gene is still there, but it's silent.

  • Boosting transcription is essentially the opposite.

  • Some chemical tags will unwind the DNA, making it easier to transcribe,

  • which ramps up production of the associated protein.

  • Epigenetic changes can survive cell division,

  • which means they could affect an organism for its entire life.

  • Sometimes that's a good thing.

  • Epigenetic changes are part of normal development.

  • The cells in an embryo start with one master genome.

  • As the cells divide, some genes are activated

  • and others inhibited.

  • Over time, through this epigenetic reprogramming,

  • some cells develop into heart cells,

  • and others into liver cells.

  • Each of the approximately 200 cell types in your body

  • has essentially the same genome

  • but its own distinct epigenome.

  • The epigenome also mediates a lifelong dialogue

  • between genes and the environment.

  • The chemical tags that turn genes on and off

  • can be influenced by factors including diet,

  • chemical exposure,

  • and medication.

  • The resulting epigenetic changes can eventually lead to disease,

  • if, for example, they turn off a gene that makes a tumor-suppressing protein.

  • Environmentally-induced epigenetic changes are part of the reason

  • why genetically identical twins can grow up to have very different lives.

  • As twins get older, their epigenomes diverge,

  • affecting the way they age and their susceptibility to disease.

  • Even social experiences can cause epigenetic changes.

  • In one famous experiment,

  • when mother rats weren't attentive enough to their pups,

  • genes in the babies that helped them manage stress were methylated

  • and turned off.

  • And it might not stop with that generation.

  • Most epigenetic marks are erased when egg and sperm cells are formed.

  • But now researchers think that some of those imprints survive,

  • passing those epigenetic traits on to the next generation.

  • Your mother's or your father's experiences as a child,

  • or choices as adults,

  • could actually shape your own epigenome.

  • But even though epigenetic changes are sticky,

  • they're not necessarily permanent.

  • A balanced lifestyle that includes a healthy diet,

  • exercise,

  • and avoiding exposure to contaminants

  • may in the long run create a healthy epigenome.

  • It's an exciting time to be studying this.

  • Scientists are just beginning to understand

  • how epigenetics could explain mechanisms of human development and aging,

  • as well as the origins of cancer,

  • heart disease,

  • mental illness,

  • addiction,

  • and many other conditions.

  • Meanwhile, new genome editing techniques are making it much easier

  • to identify which epigenetic changes really matter for health and disease.

  • Once we understand how our epigenome influences us,

  • we might be able to influence it, too.

Here's a conundrum:

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B2 US TED-Ed epigenetic epigenome dna genome chemical

【TED-Ed】How the choices you make can affect your genes - Carlos Guerrero-Bosagna

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    蔡昀倢 posted on 2016/06/29
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