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October 24, 2012--------News Archive Return to: News Alerts

The duplication of a gene results in an additional copy free from selective pressure.

One view is that this allows the new copy of the gene to mutate without bad
consequences – a freedom that allows for the mutation of novel genes with
the potential to increase the fitness of the organism or code for a new function.

Another view is that both copies are equally free to accumulate degenerative mutations,
as long as defects are complemented in either copy. This leads to a neutral
"subfunction" where the function of the original gene is shared by the two copies.

Source: Wikipedia, the free encyclopedia

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How New Genes Are Created

Scientists have long wondered how living things evolve new functions from a limited set of genes. One popular explanation is that genes duplicate by accident; the duplicate undergoes mutations and picks up a new function; and, if that new function is useful, the gene spreads

"It's an old idea and it's clear that this happens," said John Roth, a distinguished professor of microbiology at UC Davis and co-author of the paper. The problem, Roth said, is that it has been hard to imagine how it occurs.

Natural selection is relentlessly efficient in removing mutated genes genes that are not positively selected are quickly lost.

Like job-seekers searching for a new position, living things sometimes have to pick up a new skill if they are going to succeed. Researchers from the University of California, Davis, and Uppsala University, Sweden, have shown for the first time how living organisms do this.

Experiments in Roth's laboratory and elsewhere led to a model for the origin of a novel gene by a process of "innovation, amplification and divergence." This model has now been tested by Joakim Nasvall, Lei Sun and Dan Andersson at Uppsala.

How then does a newly duplicated gene stick around long enough to pick up a useful new function that would be a target for positive selection? His observation, published Oct. 19 in the journal Science, closes an important gap in the theory of natural selection.

In the new model, the original gene first gains a second,
weak function alongside its main activity — just as an auto
mechanic might develop a side interest in computers.

If conditions change — such that the side activity becomes
important, then selection of this side activity favors
increasing expression by the old gene.

For example, in the case of the mechanic, a slump in the
auto industry or boom in the IT sector might lead her
to hone her computer skills and look for an IT position.

The most common way to increase gene expression
is by duplicating the gene, perhaps multiple times.
Natural selection then works on all copies of the gene.
Under selection, the copies accumulate mutations and
recombine. Some copies develop an enhanced side
function. Other copies retain their original function.

Ultimately, the cell winds up with
two distinct genes,
one providing each activity —
and a new genetic function is born.

Nasvall, Lei and Andersson tested this model using the bacterium Salmonella.

The Salmonella bacteria carried a gene involved in making the amino acid histidine that had a secondary, weak ability to contribute to the synthesis of another amino acid, tryptophan. In their study, they removed the main tryptophan-synthesis gene from the bacteria and watched what happened.

After growing the Salmonella bacteria for
3,000 generations on a culture medium without
tryptophan, they forced the bacteria to evolve a new
mechanism for producing tryptophan.

What emerged was a tryptophan-synthesizing activity
provided by a duplicated copy of the original gene.

"The important improvement offered by our model
is that the whole process occurs under constant
— there's no time off from selection
for the extra copy to be lost."

John Roth

Professor, microbiology, UC Davis and co-author

The work was supported by the Swedish Research Council and the National Institutes of Health.
About UC Davis

For more than 100 years, UC Davis has engaged in teaching, research and public service that matter to California and transform the world. Located close to the state capital, UC Davis has more than 32,000 students, more than 2,500 faculty and more than 21,000 staff, an annual research budget that exceeds $684 million, a comprehensive health system and 13 specialized research centers. The university offers interdisciplinary graduate study and more than 100 undergraduate majors in four colleges — Agricultural and Environmental Sciences, Biological Sciences, Engineering, and Letters and Science. It also houses six professional schools — Education, Law, Management, Medicine, Veterinary Medicine and the Betty Irene Moore School of Nursing.

Original article: http://news.ucdavis.edu/search/news_detail.lasso?id=10379