TV Program Description
Original PBS Broadcast Date: October 16, 2007
Scientists have long puzzled over the different fates of
identical twins: both have the same genes, yet only one may
develop a serious disease like cancer or autism. What's going
on? Does something else besides genes determine who we are?
NOVA explores this startling possibility in this program.
The "something else" turns out to be a network of chemical
switches that sit on our DNA, turning genes off and on. Called
collectively the epigenome, the switches appear to play a
major role in everything from how our cells keep their
identity to whether we contract dread diseases. Epigenetic
switches may even help mold our personalities—or so it
appears to Canadian researchers studying a group of
epigenetically modified rats.
"We're in the midst of probably the biggest revolution in
biology, which is going to forever transform the way we
understand genetics, environment, the way the two interact,
and what causes disease," says Mark Mehler, Professor of
Neurology at Albert Einstein College of Medicine. "It's
another level of biology, which for the first time really is
up to the task of explaining the biological complexity of
life."
In this program, NOVA reveals the clues that have led
scientists to this new picture of genetic control and
expression. One such clue is the surprisingly modest number of
genes that turned up when technology made it possible to map
the human genome. The Human Genome Project was originally
expected to find at least 100,000 genes defining the human
species. Instead the effort yielded only about
20,000—about the same number as in fish or
mice—too few, some believe, to account for human
complexity.
Researchers now suspect that it's how genes are regulated that
distinguishes species. What turns them on and off? Among other
things, epigenetic switches (though not all switches are
epigenetic—see
Gene Switches).
Another clue is that a single abnormality in a chromosome may
result in two completely different diseases, depending on
whether the defect is inherited from the mother or the father.
The different fates may be due to different settings of
epigenetic switches.
And still another clue comes from a strain of mice that eats
without limit if given the chance, which leads to obesity,
diabetes, and cancer. Amazingly, their young can be rendered
slim, healthy, and longer-lived through a change in diet that
leaves their genes intact but alters their epigenetic switches
(see
A Tale of Two Mice).
The program closes at the controversial cutting edge of this
burgeoning new field. At the M. D. Anderson Cancer Center in
Houston, Texas, researchers are investigating epigenetic means
to treat a deadly form of leukemia (see
Epigenetic Therapy).
In Washington State, a researcher finds that a toxin given to
rats still affects their offspring four generations later,
without producing any changes in their genes. And in Sweden, a
study of historical records seems to show that the lifespan of
grandchildren is affected by their grandparents' access to
food.
Might these effects be epigenetic? Might our experiences, by
changing our epigenomes, literally change the fate of our
offspring ... and their offspring ... and theirs in
turn? And might our own states of health owe something to the
diets and exposures of our forebears?
Some researchers are already convinced. "You live your life as
a sort of ... guardian of your genome," says Marcus Pembrey of
the Institute of Child Health at University College London, a
co-investigator in the Swedish study. "It seems to me you've
got to be careful of it because it's not just you. You can't
be selfish ... you can't say, 'Well, I'll smoke' or 'I'll do
whatever it is because I'm prepared to die early.' You're also
looking after it for your children and grandchildren...."
Epigenetics, Pembrey says, "is changing the way we think about
inheritance forever."
Program Transcript
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