Berlin, January 1 : An international team of scientists has directly measured for the first time the speed with which new mutations occur in plants, thus capturing evolution in the act.

The team comprised of scientists from the Max Planck Institute for Developmental Biology in Tubingen, Germany, and Indiana University in Bloomington, US.

Their findings shed new light on a fundamental evolutionary process. They explain, for example, why resistance to herbicides can appear within just a few years.

"While the long term effects of genome mutations are quite well understood, we did not know how often new mutations arise in the first place," said Detlef Weigel, director at the Max Planck Institute.

It is routine today to compare the genomes of related animal or plant species.

Such comparisons, however, ignore mutations that have been lost in the millions of years since two species separated.

The teams of Weigel and his colleague Michael Lynch at Indiana University therefore wanted to scrutinize the signature of evolution before selection occurs.

To this end, they followed all genetic changes in five lines of the mustard relative Arabidopsis thaliana that occurred during 30 generations.

In the genome of the final generation, they then searched for differences to the genome of the original ancestor.

The painstakingly detailed comparison of the entire genome revealed that in over the course of only a few years some 20 DNA building blocks, so called base pairs, had been mutated in each of the five lines.

"The probability that any letter of the genome changes in a single generation is thus about one in 140 million," explained Michael Lynch.

To put it differently, each seedling has on average one new mutation in each of the two copies of its genome that it inherits from mum and dad.

To find these tiny alterations in the 120 million base pair genome of Arabidopsis was akin to finding the proverbial needle in a haystack, according to Weigel.

"To ferret out where the genome had changed was only possibly because of new methods that allowed us to screen the entire genome with high precision and in very short time," he added.

In a collection of only 60 million Arabidopsis plants, each letter in the genome is changed, on average, once.

Apart from the speed of new mutations, the study revealed that not every part of the genome is equally affected.

With four different DNA letters, there are six possible changes, but only one of these is responsible for half of all the mutations found. (ANI)