Thirty mutations are passed from each parent to their child, a finding that affects evolution and medical research, University of Montreal researchers found.

The finding revises the timescale used to calculate the number of generations separating humans from other species, the university said Monday in a release.

A person's genetic code is made up of 6 billion pieces of information, called nucleotides -- 3 billion coming from each parent, said co-lead author Philip Awadalla of the university's medical faculty.

Based on indirect evolutionary studies, "we had previously estimated that parents would contribute an average of 100-to-200 mistakes in these pieces of information to their child," Awadalla said. "Our genetic study, the first of its kind, shows that actually much fewer mistakes -- or mutations -- are made."

The study was published in Nature Genetics.

Because mutations play a role in the evolutionary process, geneticists will revise the number of generations separating humans from genetic relatives such as apes, Awadalla said.

"In principle, evolution is happening a third as slowly as previously thought," Awadalla said.

The researchers examined the complete genomes of two families consisting of a mother, father and their child.

The study also allowed the team to determine whether men contribute more mutations to their offspring than women, based on the theory that men produce millions more gametes than women. Awadalla said the research showed a wide variation on mutations between the two families.

"This doesn't mean that we're throwing the theory out the window," he said. "It simply means that the mutation rate is extremely variable from individual to individual, or even that some people have mechanisms that reduce the likelihood of mutations."

Researchers will have to conduct studies with more families to better understand how variable the individual mutation rate is, Awadalla said.

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