What separates humans from chimps may not be in our genes, but rather in how they are spliced, new Canadian-led research suggests.

Chimpanzees and humans share nearly 99 per cent of genes, even though they differ greatly in the way they look and behave. In a study published Wednesday in the journal Genes and Development, researchers suggest these differences could be linked to differences in the way genetic material is spliced to create proteins.

Researchers say the difference between man and chimp may be in the way genes are spliced. This undated picture shows Washoe, a female chimpanzee believed to be the first non-human to acquire human language.
(AP Photo/Central Washington University)

University of Toronto professor Benjamin Blencowe and his team, which included graduate student researcher John Calarco and colleagues from the United States, compared brain and heart tissue from humans and chimps. They found that at least four per cent of genes had different splicing patterns. 

The differences affected a number of functions, including gene regulation and defence against disease.

Blencowe said such findings, "could help people try to pin down the biological processes that result in humans displaying certain diseases that are not found in chimpanzees." For example, he said, chimpanzees are not susceptible to Alzheimer's disease.

Blencowe told CBC News that it was "quite surprising" to discover that the alternative splicing process differed so significantly between humans and chimpanzees.

"Alternative splicing process is an additional source of diversity in gene expression between humans and chimpanzees," he explained. He said the results suggest splicing could play a defining role in establishing differences between humans and chimpanzees.
 
The researchers also examined a gene that is tentatively linked to aging-related diseases and spliced differently between chimps and humans. The gene codes for an enzyme that protects against oxidative damage, which is linked to aging effects such as neurodegeneration, and was found to be expressed at a higher level in chimps than in humans.

Blencowe said the researchers hope to also apply such comparisons of alternative splicing to study differences between human and chimpanzee brains, for example in relation to cognition.