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Evolution and Chickens: Genetic Differences Observed On Shorter Time Scale, Researchers Say

Oct 28, 2015 03:44 PM EDT
White Plymouth Rock Chickens
Selective mating within a population of Plymouth Rock chickens (pictured here) has made modern individuals ten times larger than some of their ancestors.
(Photo : Virginia Tech/John McCormick)

After studying a population of modern chickens, Oxford University researchers have determined that evolution can happen 15 times faster than previously thought. During their study, researchers observed two mutations in the species within only 50 short years. 

"Our observations reveal that evolution is always moving quickly, but we tend not to see it because we typically measure it over longer time periods," Professor Greger Larson, lead researcher of the Oxford University team, said in a news release. "Our study shows that evolution can move much faster in the short term than we had believed from fossil-based estimates. Previously, estimates put the rate of change in a mitochondrial genome at about two percent per million years. At this pace, we should not have been able to spot a single mutation in just 50 years, but in fact we spotted two."

For their study, researchers examined a well-documented, Plymouth Rock chickens with a 50-year pedigree developed at Virginia Polytechnic Institute by Professor Paul Siegel. Plymouth Rock chickens are a dual-purpose poultry breed known for their meat production and year-round egg laying. Oxford researchers also analyzed DNA from blood samples of 12 chickens of the same generation, according to the release.

Overall, researchers concluded that modern chickens are ten times larger than their ancestors. This is a result of inbred lines that were established when farmers began selectively mating the animals in an attempt to increase their size, an approach that started in 1957. Knowing this, researchers traced the most distant maternal lines when analyzing DNA samples to get a more accurate representation of the population's evolution and, ultimately, determine how mitochondrial DNA was passed down to daughters from their mothers.

In doing so, researchers also revealed that "parental leakage," which involves mitochondria being passed to offspring from fathers rather than mothers, is not as rare as scientists thought. In fact, when examining the genetic sequences of the chickens' ancestry, researchers discovered a single instance of mitochondrial DNA being passed down from a father. Their findings were recently published in the journal Biology Letters.

"The one thing everyone knew about mitochondria is that it is almost exclusively passed down the maternal line, but we identified chicks who inherited their mitochondria from their father, meaning so-called 'paternal leakage' can happen in avian populations," Dr. Michelle Alexander, lead author of the study from the University of York, explained in a statement. "Both of these findings demonstrate the speed and dynamism of evolution when observed over short time periods."

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