Epigenetics is a new branch of biology that is interested (among other things) in the changes of expression in genes transmitted during cell division, sometimes for generations, independently of any change in the DNA sequence. Researchers from the CNRS and INRA created a unique population of so-called “epiRILs” lines (epigenetic recombinant inbred lines) several years ago, in the model plant Arabidopsis. These lines have the same genome (or almost), although they exhibit many epigenetic differences throughout the genome. These differences express themselves through methyl groups that can be grafted onto DNA. Without transforming the genetic code, these groups are superimposed on it and therefore change the structure of the DNA strands, and thus gene expression.

These biologists, together with researchers from Inserm and the Genoscope, now provide evidence that a small number of epigenetic variations between lines are alone responsible for over 90% of the heritable differences of two complex characters: flowering date and size of the primary root. In addition, the researchers show that some of these epigenetic variations are also found in natural populations of Arabidopsis.

These observations call into question the dogma that genetic differences between individuals can be sought for in their genome sequence alone. They thus possibly provide part of the answer to the “missing heritability” problem. Indeed, many human genetics analyses today only demonstrate a small fraction of the heritability observed for diseases [1] or complex characters.

[1] This is especially the case in multiple sclerosis and Crohn’s disease