Genetic 'Arms Race' Helped Shape Human Genome

Scientists have discovered evidence of a hidden war between rival elements within the genomes of primates that likely helped shape the human genome over time, according to new research.

The arms race in question is between mobile DNA sequences known as "retrotransposons," or "jumping genes," and the genes that have evolved to control them. But over time, the jumping genes have formed mutations that allow them to escape their repressors when needed, driving the evolution of new repressor genes, thereby causing more jumping gene "resistance," according to the study.

The findings, published in the journal Nature, indicate that repressor genes, designed to shut down jumping genes, have been co-opted to regulate the other parts of the genome.

This back and forth rivalry has helped foster the evolution of complex regulatory networks that orchestrate the activity of genes in every cell of our bodies.

"We have basically the same 20,000 protein-coding genes as a frog, yet our genome is much more complicated, with more layers of gene regulation," lead author Sofie Salama, a research associate at the University of California, Santa Cruz Genomics Institute, said in a statement. "This study helps explain how that came about."

Jumping genes are believed to be remnants of ancient viruses that infected early animals way before humans evolved. They insert themselves into the genome as they replicate, and depending on where they jump to, can disrupt normal genes and cause disease, or remain neutral and simply add to the overall size of the genome.

Scientists have determined that jumping genes account for at least half of the human genetic code.

"There have been successive waves of retrotransposon activity in primate evolution, when a transposable element changed to become expressed and replicated itself throughout the genome until something turned it off," said Salama.

"We've discovered a major mechanism by which the genome is able to shut down these mobile DNA elements."