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Research in chickens has provided direct evidence of "paternal leakage" in which mitochondria are inherited from the father instead of the mother

Scientists from the University of Oxford discovered two mutations that occurred in the mitochondrial gene of the birds during fifty years, which shows that the rate of evolution is greater than what was commonly thought according to which changes in the mitochondrial genome occur at a rate of two percent per million years.

A selective mating approach in a chicken population that began in 1957 led to a 10-fold difference in size between chickens. Photo Credit: Virginia Tech/ John McCormick
A selective mating approach in a chicken population that began in 1957 led to a 10-fold difference in size between chickens. Photo Credit: Virginia Tech/ John McCormick

A new study conducted in chickens has challenged the popular hypothesis that evolution is observable over long periods of time. Through the study of individual chickens that were part of a long-term breeding program, the researchers led by Prof. Gregor Larsson from the Archaeological Research Laboratory at the University of Oxford were able to discover mutations that occurred in the mitochondrial genomes of birds in just 50 years.

For a long time, scientists estimated that the rate of change in the mitochondrial genome for our world is faster than 2% per million years. The evidence for these mutations shows that the rate of evolution in this family tree is 15 times faster. By sequencing the genome along the lineage, the researchers discovered that a single version of mitochondrial DNA was passed down from the father.

This is a surprising discovery that shows that the process known as "paternal leakage" is not as rare as previously thought. The study was published in the journal Biology Letters.
Using a documented lineage of white Plymouth Rock chickens developed at Virginia Tech by Prof. Paul Siegel, the researchers were able to identify how mitochondrial DNA was passed from mother to daughter within the populations. They took a blood sample from 12 chickens of the same generation and whose sacrifice between them is as small as possible. Knowing that these populations started from seven dynasties that partially interbred among themselves.

Selective fertilization within the populations began in 1957, resulting in a 10-fold difference in size between the two groups at 56 days of age.

Lead researcher Prof. Larsson says: "Our observations reveal that evolution always moves fast but we tend not to see it because we measure it over long periods of time. Our research has shown that evolution can move much faster in a short period of time than we estimated from examining fossils. Earlier, we believed that the rate of change would allow us to observe one mutation over fifty years, but in fact we discovered two."

According to the paper, there is now significant evidence of differences between the long-term and short-term estimates of mitochondrial changes. One of the theories trying to explain the phenomenon, and which the researchers claim is preferable, is that the mitochondrial DNA evolved in a non-neutral way, that purifying selection is carried out, and that negative mutations are removed faster than beneficial or neutral mutations. So far, there have been very few studies of the short-term evolution of mitochondria that included both mutation rate and paternal leakage. There is now direct evidence that mitochondria are not always inherited from the mother.

Lead researcher Dr Michelle Alexander from the University of York said: "The only thing everyone knew about mitochondria is that it is always passed on through the maternal line, but we identified chicks that inherited mitochondria from their father instead of their mother. This means that the same "paternal leakage" can occur in an avian population. These two findings demonstrate the speed and dynamics of evolution when viewed in short time frames."

to the notice of the researchers

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