Canadian researchers have unraveled a genetic "code within a code" that helps explain how the instructions for building complex organisms, like humans, can be found in a small number of genes.

University of Toronto scientists Brendan Frey and Benjamin Blencowe said they have found a hidden code in DNA that helps explain how a small number of genes can contain instructions for a larger number of proteins and structures.

When researchers fully sequenced the human genome in 2004, they were surprised at how few genes humans actually have.

"Human DNA has 22,000 genes. That might seem like a lot, but not when you consider that a poplar tree has 45,000," said Frey, in a statement.

Frey said his team, including Blencowe and Yoseph Barash, found a second level of information that the cells of living organisms use to create a larger set of instructions.

"We discovered a hidden code within DNA that living cells use to turn 20,000 genes into hundreds of thousands of genetic messages, by rearranging their parts," he said.

Barash and Frey, who is also a professor of computer science and engineering, created a computer program that analyzes DNA to find "code words" in the genome.

The code words together are called the "splicing code," containing the biological information needed to splice together different parts of the genetic code in different orders to generate a greater number of messages.

"For example, three neurexin genes can generate over 3,000 genetic messages that help control the wiring of the brain," said Frey.

Neurexin is a protein that glues together the connections between nerve cells in the brain.

Frey said their work is the result of a close collaboration between computer scientists and experimental biologists.

"Understanding a complex biological system is like understanding a complex electronic circuit. Our team 'reverse-engineered' the splicing code using large-scale experimental data generated by the group," he said.

The research was the cover story in this week's issue of the journal Nature.