For more than a century, Gregor Mendel’s pea plant experiments have defined how traits pass from parent to offspring. But a new study in mice suggests that some inherited traits do not follow those classic rules at all.
Researchers at Johns Hopkins Medicine and Texas A&M University found that about 7% of epigenetic inheritance patterns they examined behaved in unexpected ways. These chemical marks on DNA, which affect how genes work without changing the genetic code itself, sometimes appeared to emerge from nowhere or follow rules never before seen in mammals.
Epigenetic marks that break the rules
Epigenetic changes are chemical modifications, such as DNA methylation, that can turn genes on or off. Unlike mutations in the DNA sequence, these marks can shift in response to environmental pressures. The study, published May 20 in Nature Genetics, looked at how these marks were passed down in mice across generations.
The team discovered hundreds of cases where the inheritance of these chemical marks did not match Mendel’s predictions. Some marks seemed to appear spontaneously, with no clear parent of origin. Others showed patterns of genomic imprinting, where whether a trait is expressed depends on which parent contributed it, not on whether the gene is dominant or recessive.
First natural paramutation found in a mammal
Perhaps the most striking finding was the identification of the first known naturally occurring paramutation in a mammal. Paramutation is a rare form of inheritance previously documented only in plants and fruit flies. In this process, one allele can instruct another allele to change its epigenetic state, and that new state is then passed to future generations.
The discovery hints that environmental influences may play a larger role in inheritance than scientists had realized. Andrew Feinberg, a Bloomberg Distinguished Professor at Johns Hopkins and co-leader of the study, noted that non-Mendelian patterns of epigenetic inheritance could allow organisms to acquire diverse or new traits more quickly than changes to the DNA sequence itself.
The research was funded by the National Institutes of Health and the National Science Foundation. It adds to a growing body of evidence that inheritance is more complex than Mendel’s laws alone can explain.
What this means for understanding inheritance
The findings do not overturn Mendel’s work, but they expand the picture. Mendel’s laws still describe how many genetic traits are passed down. But this study shows that epigenetic marks can follow their own rules, sometimes appearing, disappearing, or changing in ways that DNA sequences cannot.
For scientists, these results open new questions about how traits evolve and how organisms adapt to their environments. If epigenetic changes can be inherited in non-Mendelian ways, then the speed and flexibility of adaptation may be greater than previously thought. The study was highlighted in an accompanying Nature brief and represents a step toward understanding the full landscape of inheritance.
