But scientists at Purdue University in Indiana have discovered the classic rules don't apply to a plant called Arabidopsis thaliana, which has bypassed genetic abnormalities carried by both parents and reverted to normal traits from the grandparents.

"This means inheritance can happen more flexibly than we thought in the past," said Robert Pruitt, a molecular geneticist at the university.

"While Mendel's laws that we learned in high school are still fundamentally correct, they're not absolute."

If the mechanism he and his colleagues discovered in the plant exists in animals, they believe it could pave a path for gene therapy to treat diseases in plants and humans.

In research reported in the science journal Nature, the scientists said they found the anomaly when they noticed normal flowers on plants that were the offspring of deformed plants.

The parents had a mutated gene that prevented its flowers from opening. But the grandparents and 10 percent of the grandchildren had normal flowers.

"If you take this mutant Arabidopsis, which has two copies of the altered gene, let it seed and then plant the seeds, 90 percent of the offspring will look like the plant, but 10 percent will look like the normal grandparents," Pruitt said in a statement.