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Thursday, May 25, 2006
Non-DNA Inheritance - A New Mechanism Discovered
The standard genetic model for the inheritance of traits is based on the transmission of genes, regions of DNA, from parents to offspring. In a new discovery, reported in Nature, researchers in France have found that a trait, in this case a spotted tail in mice, can be passed to offspring even if the DNA variant for that trait is not present.

They discovered that a mutation in the Kit gene would be lethal if a mouse were to inherit copies of that gene from both parents. If they inherited one mutant gene and one normal gene, then they would develop a spotted tail. But offspring from these crosses that inherited two normal copies also developed the spotted tail, and that seemed to defy the basic assumption of genetic inheritance.

Upon further investigation, they discovered that the sperm cells from the male parent contained not only the paternal DNA, but also some RNA molecules that had been produced before the sperm cell was fully formed. Messenger RNA (mRNA) is formed from the DNA template and goes on to act as the template for making proteins, so any mutation in the DNA will be reflected in the mRNA molecule. Apparently, some mutant mRNA was formed in the male and deposited in the sperm cells, even though some of those sperm cells had normal DNA. The mutant mRNA was them transmitted to the egg during fertilization where it led to the development of the spotted tail.

This phenomenon had been noticed in several plant species, but there was no real understanding of the process involved. There are also some intriguing hints that this may be a widespread phenomenon, including being an explanation for some of the inheritance patterns found in human diabetes.

It is well known that there are many factors that intervene between the DNA in our cells, and the final traits that we exhibit - factors that determine when and where genes are turned on, and how the proteins that they code for are assembled. This is the field of epigenetics, the study of all these non-DNA-based determinants of how traits develop. This study opens yet another door of possibilities for new explanations in this rapidly developing field.

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