Researchers at the University of Texas recently witnessed introns multiplying in a genome. It's a rare evolutionary event they say may help scientists better understand gene expression and the evolution of new species.

"Until now, the only way researchers could track the evolution of introns was through phylogenetic analysis which is examining the evolutionary relationships among sets of related organisms," researcher Scott Stevens, an associate professor of molecular biosciences at Texas, explained in a news release. "Our work is the first experimental verification that shows how introns can be transposed into an organism."

Introns are non-coding DNA sequences found in genes. Scientists used to call these sequences "junk DNA," as it was erroneously believed that they were genetic dead weight.

While the sequences do not code for functional molecules or proteins, new research has shown that introns do play a role in dictating gene expression.

When eukaryotes first diverged from bacteria and paved the way for complex life, the eukaryote genome took on an influx of introns. Simpler life forms, like yeast, have excised their introns, but most complex organisms, like mammals, continued to acquire more.

Some 40 percent of the human genome is made up of introns, of which there are at least 2,000.

Stevens and his research partner, Sijin Lee, a former graduate student, monitored several generations of more than half a trillion yeast, Saccharomyces cerevisiae. They designed a unique assay to monitor the loss or gain of introns. During the development of hundreds of billions of yeast, the researchers identified just two instances of intron addition.

Twice, an intron was added to a new gene. Most of the time, introns are spliced out of the DNA and the remaining RNA is translated into protein. In these two instances, the cell did the opposite, allowing the introns into the RNA code. The newly accumulated introns constituted a genetic change.

"We showed in this project that introns continue to be gained, although infrequently at any point in time," explained Stevens. "But can introns drive evolution? If these sequences give organisms a selective advantage and become fixed in a population, others have shown that it can be a major factor in the creation of new species."

Intron accumulation could also explain the development of human diseases like cancer.

"We are continuing this work to further understand how this process impacts our genetic history, our future, and the prospects of curing disease," Stevens added.

The researchers published their latest findings in the journal PNAS.