mysterious loophole linked to the mitochondrial DNA might have the answer to
why women live longer than their male counterparts.
The mitochondria, which are
called the "powerhouses of the cell" comprises of DNA which is different from
the nuclear DNA. The mitochondrial DNA is inherited from the mother to the
child without any contribution from the dad.
According to a new study
published in the journal Current Biology
this direct line of mitochondrial inheritance may allow harmful mutations to
Natural selection normally ensures that harmful mutations are kept
to the barest minimum by not passing it down to future generations.According to
study researcher Damian Dowling, evolutionary biologist, Monash Univeristy,
Australia, the mitochondrial DNA mutations, that are usually harmless to
females, pass through the gates of natural selection and find their way to the
next generation.††††††††††† This usually
results in a lot of mutations, that are harmful to the males and affect their
longevity, but which are harmles to women.
The phenomenon, nicknamed
"mother's curse", was tested on the fruit fly drosophila melanogaster. It has
always been believed that women outlive men because they take lesser risks than
men during life's journey and also because the male hormone testosterone is
linked to reduced longevity.But insects have no testosterone and are not prone
to take risks like humans, so it was prudent to start this particular study
Mitochondrial DNA was taken from
thirteen different fruit fly populations from around the world and inserted
into another group of flies with the same cellular DNA. This made sure that in
these flies only the mitochondrial DNA differed.
It was found that in all the
strains of flies studied, the males suffered in terms of ageing and longevity
while the female parameters did not suffer in any way. This observation
provides strong evidence that the mitochondrial genome is riddled with loads of
deleterious mutations that affect male aging but does not harm females.
The inheritance of the
mitochondrial DNA occurs in the same manner in all species and therefore, this
finding is expected to be true of humans too.However, despite this gloomy note,
all may not be lost for men as Dowling and her colleagues are now seeking to
uncover the genes in the nuclear DNA of men that may actually compensate for
their mitochondrial handicap.