October 27, 2015
A new study of
chickens overturns the popular assumption that evolution is only visible over
long time scales. By studying individual chickens that were part of a long-term
pedigree, the scientists led by Professor Greger Larson at Oxford University's
Research Laboratory for Archaeology, found two mutations that had occurred in
the mitochondrial genomes of the birds in only 50 years. For a long time
scientists have believed that the rate of change in the mitochondrial genome
was never faster than about 2% per million years. The identification of these
mutations shows that the rate of evolution in this pedigree is in fact 15 times
faster. In addition, by determining the genetic sequences along the pedigree,
the team also discovered a single instance of mitochondrial DNA being passed
down from a father. This is a surprising discovery, showing that so-called
'paternal leakage' is not as rare as previously believed.
The study is
published in the online early version of the journal, Biology Letters.
Using a
well-documented 50-year pedigree of a population of White Plymouth Rock
chickens developed at Virginia Tech by Professor Paul Siegel, the researchers
reconstructed how the mitochondrial DNA passed from mothers to daughters within
the population. They did this by analysing DNA from the blood samples of 12
chickens of the same generation using the most distantly related maternal
lines, knowing that the base population had started from seven partially inbred
lines. A selective mating approach within the population started in 1957,
resulting in what is now an over tenfold difference in the size of the chickens
in the two groups when weighed at 56 days old.
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