At Johns Hopkins University, scientists have discovered that roughly 7% of inherited epigenetic marks defy the foundational rules of genetics that have guided biology for over 160 years, fundamentally challenging our understanding of how traits pass from parents to children.
For more than a century, Gregor Mendel's laws of inheritance have explained how genetic traits move through families. But a new federally funded study published May 20 in Nature Genetics reveals that the story is far more complex than dominant and recessive alleles alone. Parents pass along more than DNA sequences to their offspring—they also transmit epigenetic changes, chemical modifications that affect how genes function without altering the underlying genetic code itself.
Researchers at Johns Hopkins University and Texas A&M University, led by Andrew Feinberg, Bloomberg Distinguished Professor across the Johns Hopkins University School of Medicine, Whiting School of Engineering and Bloomberg School of Public Health, examined three generations of mice to track DNA methylation patterns. The first generation included 26 mice, followed by 34 offspring in the second generation and 19 in the third. By analyzing large portions of the mouse genome and monitoring 12 previously recognized patterns of inherited DNA methylation, the team uncovered 522 cases—representing about 7% of the epigenetic inheritance patterns examined on non-sex chromosomes—that behaved in unexpected ways.
Among the most startling discoveries were 54 rare "emergent" inheritance events in which traits appeared in offspring without being present in either parent. In one striking example, two mice lacking methylation on a specific allele produced offspring where both copies of that allele carried methylation marks. "The methylation seemingly appeared out of nowhere," Feinberg explains. These findings suggest that some epigenetic traits emerge through mechanisms that scientists are only beginning to understand.
The study also identified imprinting patterns—cases where whether an allele is active depends on whether it was inherited from the mother or father—in five additional genes. Even more remarkably, the researchers documented the first evidence of paramutation, a rare inheritance phenomenon previously observed in plants and flies but never before confirmed in mammals, occurring in a gene called Capn11 that plays an important role in sperm development.
The implications stretch far beyond laboratory curiosity. Non-Mendelian epigenetic inheritance could provide organisms with a faster pathway to acquire diverse or new traits in response to environmental pressures than mutations to DNA sequences themselves. This means that environmental influences may shape inheritance patterns in ways that bypass the slow machinery of genetic mutation, allowing species to adapt more rapidly to changing conditions.
The research, supported by the National Institutes of Health and the National Science Foundation, was conducted by investigators including co-corresponding authors David Threadgill, Regents professor at Texas A&M, and Kasper Hansen, professor of biostatistics at Johns Hopkins Bloomberg School of Public Health. Johns Hopkins graduate student Adam Davidovich developed new laboratory and computational approaches that allowed genomic and methylation data to be studied simultaneously, creating tools that may open new avenues for understanding inheritance across biological systems.
These discoveries suggest that biology's foundational inheritance rules remain incomplete, and that the mechanisms by which parents shape their children's traits extend far beyond what Mendel could have imagined.