- Scientists have discovered what they
believe may be the molecular basis of evolution.
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- They may have found out what actually
happens to an organism's genes that enables its offspring to adapt and
change - that is to evolve into new types of living creatures.
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- The researchers at the University of
Chicago say that although an organism's DNA is changing over time, many
of the individual, small genetic variations just accumulate and only become
noticeable when that organism is under environmental stress.
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- You can look at it this way: while an
animal may be perfectly adapted to its environment, behind the scenes redundant
copies of its genes are mutating.
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- Only when the creature's environment
alters and it needs to adapt to the changing conditions do these mutations
come to the fore.
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- Essence of evolution
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- Most mutations will be harmful and will
not help the creature survive better. But some mutations just might provide
an edge.
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- This is the essence of evolution - creatures
have to adapt to changing conditions. Those that have an edge will survive
- those that do not will perish.
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- "For the first time we have a molecular
mechanism that explains how organisms that have stuck to the same shape
for eons can evolve new traits that help them adapt to changing conditions,"
says Susan Lindquist, professor of molecular genetics & cell biology
at the University of Chicago.
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- The way cells do this is by using molecules
called heat shock proteins, in particular Hsp 90. Usually this molecule
helps other molecules in the cell to cope with heat.
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- But when an organism is under particular
stress and has to cope with a changing environment, it appears that Hsp
90 gets called away from its normal duties and many of the genetic mutations
that had hitherto been masked suddenly break out.
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- These can then be passed onto the organism's
offspring to produce changes in body plan.
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- New environment
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- "This sounds like a very bad thing,
and no doubt it is for most of the individuals," says Lindquist. "But
for some, the changes might be beneficial for adapting to a new environment."
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- Lindquist and Suzanne Rutherford, a postdoctoral
fellow, demonstrated that reducing levels of Hsp 90 allowed natural genetic
abnormalities hidden in fruit fly populations to suddenly appear.
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- They produced flies with eyes of different
colours; deformed in shape or absent; flies with misshapen legs; flies
with small or absent wings, and so on.
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- Lindquist speculates that Hsp 90 may
be a key player in controlling the alternation between long periods of
genetic stability and the sudden bursts of change seen in the fossil record
during times when the Earth was undergoing major climate changes.
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- "The way that Hsp 90 covers and
uncovers hidden genetic variations provides a very plausible molecular
mechanism for evolution, but proving that it actually works over long timescales
will be no easy task," she says.
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