An extraordinary discovery by researchers at Purdue University, Indiana, USA, indicates that Mendelian rules of inheritance are not as straightforward as was previously thought. The accidental findings have shown that plants seem to be able to bypass the harmful mutant genes inherited from their parents by reverting to the genetic code of their grandparents.

In Nature, Robert Pruitt and colleagues showed that despite Arabidopsis parents having two mutant copies of HOTHEAD, which leads to fused floral structures, 10% of the offspring had normal flowers. These progeny had rewritten one or both copies of the mutant gene, thereby reverting to the ancestral sequence of their (normal) grandparents.

The team could find just one explanation: the “...plants keep a cryptic copy of everything that was in the previous generation, even though it doesn't show up in the DNA...” says Pruitt (ScienceDaily, 23 March 2005). The most likely candidate is RNA, inherited from previous generations and used somehow as a 'backup' for correcting genes. “This demonstrates a parallel path of inheritance that we've overlooked for 100 years.” (The Sunday Times, 27 March 2005).

Other faulty genes were also found to revert to their ancestral form, indicating that templates for many, if not all, genes are inherited.

Geneticist Elliot Meyerowitz, of the California Institute of Technology, commented that he wouldn't be surprised if the new DNA editing mechanism was present in people too (The Washington Post, 23 March 2005).