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  • Posted 09.08.09
  • NOVA scienceNOW

In this video segment adapted from NOVA scienceNOW, learn about the epigenome, a set of chemical switches that interact with DNA and affect how some genes are expressed. The epigenome tells cells what they will be and how they will function. Researchers in the field of epigenetics are studying mice as well as humans to determine how gene expression is affected by environmental factors and lifestyle choices. What they've learned is helping them explain differences that can appear over time in identical twins, and more broadly, in the general population.

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NOVA scienceNOW Epigenetics
  • Media Type: Video
  • Running Time: 5m 36s
  • Size: 16.7 MB
  • Level: Grades 9-12

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Source: NOVA scienceNOW: "Epigenetics"

This media asset was adapted from NOVA scienceNOW: "Epigenetics".


Nearly every cell in a person's body contains DNA with an identical sequence of nucleotide bases. These double-stranded molecules carry the genetic instructions that encode proteins and enable cells to reproduce and perform specific functions. But the individual members of the genome—the sum total of DNA contained in an organism—aren't self-directed. Like actors in a troupe, they need to be assigned roles before the script can be acted out. The epigenome is a set of chemical switches that control gene expression within a cell. It's like a second layer of information that tells genes how to act. By turning some genes on and leaving some genes off, it directs certain cells to become brain cells, others hair cells, and so on.

Epigenetics is an emerging scientific field. Research focuses on the chemical changes that affect gene expression but do not alter the base sequence of DNA. These chemical changes include methylation, the addition of a methyl group to certain nitrogen bases. Researchers are studying these patterns of gene expression, which are passed on from parent to offspring. They are also studying how environmental factors can change the way in which genes are expressed. A growing body of evidence suggests that a wide variety of illnesses and behaviors may be linked to epigenetic mechanisms. These include various cancers, cognitive dysfunction, and autoimmune diseases. The environmental factors suspected of altering epigenetic processes include heavy metals, pesticides, tobacco smoke, and radioactivity.

The video segment demonstrates how epigenetic research is contributing to our understanding of diseases like cancer. Changes in epigenetic programming can cause genes to be turned on all the time, rather than being switched on and off based on the body's needs. This may lead to over-expression and the uncontrolled cell division typical of cancers. In some cases, the problem is precisely the opposite: tumor-suppressing genes, which normally restrict cell division, are switched off. The goal of epigenetic cancer therapy is not to kill cells but rather to change the instructions they are given.

Epigenetic research may also help realize the potential of stem cells for medical applications. One of the primary challenges scientists face is not being able to control how stem cells differentiate into a specific tissue or cell type. They recognize that turning genes on and off plays a key role in differentiation, but they are still searching for the mechanism that controls the switch. Because a stem cell can develop into any tissue or cell type, this suggests that its DNA may be open to epigenetic modification. If scientists could understand which regions of a stem cell's genome are switched on and off and control how this happens, they may be able to reliably deliver stem cells to patients with specific cell or tissue transplant needs.

To learn how environmental stress may trigger life-extending genes into action, check out Longevity Genes.

To learn more about the ways in which stem cells can be used to treat and help cure diseases in humans, check out Therapeutic Uses of Stem Cells.

Questions for Discussion

    • In what way do the brown and yellow mice shown in the video differ? Why is this so?
    • Explain DNA methylation. How does this process influence cellular function?
    • Explain how two genetically identical twins are not really identical.
    • Explain why DNA from an older twin set differs more significantly than the DNA of a younger twin set. What factors could account for this?

Resource Produced by:

					WGBH Educational Foundation

Collection Developed by:

						WGBH Educational Foundation

Collection Credits

Collection Funded by:

						Amgen Foundation

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