Mendel's famous laws of heredity, established over a century ago, may not be as universal as once thought. A recent study on mice reveals that certain traits can be passed from one generation to another without following the classic rules of genetics, thanks to chemical modifications that act on DNA without altering its sequence.
These modifications, called epigenetic, include DNA methylation, a process where chemical groups attach to certain parts of the genome to activate or deactivate genes. Until now, it was thought that these marks were reset at each generation, but new observations indicate that they can be inherited in unexpected ways.
A team of researchers investigated this phenomenon by analyzing tissue samples from three generations of mice, aged 4 to 6 months. Using long-read sequencing techniques, they were able to track both genetic variations and methylation patterns in 26 individuals from the first generation, 34 from the second, and 19 from the third.
The results show that about 7% of inherited methylation patterns do not follow Mendel's rules. Some cases are particularly surprising: methylation marks appear in offspring while they were absent in both parents. As lead researcher Andrew Feinberg says, 'methylation seems to appear out of nowhere'.
Another rare mechanism, called paramutation, has been observed for the first time in a mammal. In the Capn11 gene, involved in sperm formation, methylation from one version of the gene can transfer to another version. This process was already known in plants and flies, but never in mice.
These discoveries change our understanding of heredity. For Kasper Hansen, co-author of the study, they encourage scientists to consider both genetic and epigenetic information to better explain how diseases and traits are transmitted. Thus, environmental factors, such as diet or stress, could influence future generations in unexpected ways.
The next step will be to apply these methods to human data. The researchers hope to reveal unusual inheritance patterns in certain families affected by diseases, and pave the way for a better understanding of the links between environment and trait transmission.