For more than a century, heredity has been framed through the tidy logic of Mendel’s pea plants: traits pass from parent to offspring by fixed genetic rules. But a new mouse study suggests that chemical marks layered on DNA can sometimes slip past those rules, carrying inherited effects in ways standard genetics does not fully explain. That does not mean the basic laws of genetics are suddenly obsolete. It does mean they may not tell the whole story. In this case, researchers found that DNA methylation, a chemical tag that can turn genes on or off without changing the DNA sequence itself, sometimes passed across generations in ways that did not follow the classic patterns of dominance, recessiveness, or simple parental contribution. Looking across three generations of mice, the team identified 522 cases on non-sex chromosomes where inherited methylation patterns broke Mendel’s rules. Those cases made up about 7% of the epigenetic inheritance patterns they tracked, a share large enough to suggest these exceptions are not just biological curiosities. “Non-Mendelian patterns of inheriting epigenetics could …