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Genetic modification makes
hermaphrodites fond of same sex
29 October, 2007
Researchers have genetically
altered tiny worms to make them
attracted to worms of the same sex.
The finding, the researchers claim,
provides evidence that sexual
orientation is “wired” in the
creatures’ nervous system.
The study by researchers at University
of Utah, the United States, examined
tiny soil worms called nematodes, or
C. elegans, most of which are
hermaphrodites that can reproduce by
themselves.
The study has been published in the
scientific journal Current Biology.
It is already known that 1in 500
nematodes develops into a male, and
these males are attracted to the
pheromones of the hermaphrodites. The
researchers had thought that this
attraction was on account of physical
changes during the development of the
worms that are unique to the males of
the species.
Now they have found that when certain
genes present in the neural network
and common to both males and
hermaphrodites were altered in
hermaphrodites, it made the
hermaphrodites seek out other
hermaphrodites. This happened even
though they possessed none of the
other physical characteristics of the
males.
Erik Jorgensen, professor of biology
at the University of Utah and leader
of the study, said in a statement,
“The conclusion is that sexual
attraction is wired into brain
circuits common to both sexes of
worms, and is not caused solely by
extra nerve cells added to the male or
female brain.”
However, the researchers cautioned
that while the results hold true for
worms, “our conclusions are narrow in
that they are about worms and how
attraction behaviors are derived from
the same brain circuit. “But an
evolutionary biologist will consider
this to be a potentially common
mechanism for sexual attraction,”
added Professor Jorgensen.
Previous research, published in the
journal Science in 2003, had showed
that the worms start out as
hermaphrodites when in the larval
stage. When
food was abundant, some of the
hermaphrodites with XX chromosome
would shed an X chromosome and become
male.
Scientists often use C. elegans as a
research model because it is easier to
study biological processes in the
microscopic worms, which mature in
days.
Nematodes, or C. elegans, are one-millimetre-long
(125th of an inch) worms that live in
soil and eat bacteria. Because the
same genes are found in many animals,
nematodes, mice, zebrafish and fruit
flies often are used as “models” for
humans in research.
Since nematode worms do not have eyes,
attraction is based only on the sense
of smell.
Hermaphrodites, having both male and
female organs and producing both eggs
and sperm, are loosely referred to as
females because they produce
offspring.
Most of the time, according to
scientists, the hermaphrodites do not
mate. But if they mate, instead of
having 200 offspring, they can have
1,200 offspring.
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