New Rules For Heredity (Non-Mendelian Inheritance of Epigenetics)

Hosted by Lester Nare and Krishna Choudhary, this episode marks Krishna’s return to the studio after paternity leave — and the timing could not be more fitting. Today’s deep dive is about inheritance: not just the classic Mendelian rules most of us learned in biology class, but the stranger, more dynamic world of non-Mendelian epigenetic inheritance. Starting from Gregor Mendel and his pea plants, Lester and Krishna rebuild the foundations of genetics from first principles: dominant and recessive alleles, Punnett squares, chromosomes, fruit flies, DNA, and the physical mechanism behind inherited traits. Then they move into the “software layer” of biology: epigenetics, DNA methylation, chromatin packaging, RNA interference, and paramutation — cases where the genetic code is present, but the cell’s machinery silences or rewrites how that code is used. The episode centers on a new Nature Genetics paper, “Non-Mendelian inheritance of DNA methylation patterns in mice,” which suggests that non-Mendelian epigenetic inheritance may be more widespread in mammals than previously understood. The conversation also covers why Oxford Nanopore sequencing made this kind of analysis possible, why methylation patterns can be hard to trace across generations, and what all of this could mean for disease risk, drug response, sex differences, evolution, and the long-running nature-versus-nurture debate. Summary Mendel’s rules — how pea plants, true-breeding lines, dominant and recessive traits, and Punnett squares gave us the first mathematical laws of inheritance. The first cracks in Mendel — how chromosomes, fruit flies, sex-linked traits, and linked genes showed that inheritance is more complicated than independent assortment. DNA as hardware, epigenetics as software — why having a gene is not the same thing as expressing it, and how methylation and chromatin packaging can silence parts of the genome. Paramutation — how one allele can change the expression state of another allele across generations, creating inheritance patterns that do not follow standard Mendelian expectations. Oxford Nanopore and the technology shift — why long-read sequencing and direct methylation detection make it possible to trace epigenetic marks back to the parent they came from. The mouse methylation paper — how researchers used collaborative cross mice to show that most methylation inheritance looks Mendelian, but a meaningful fraction appears to follow stranger non-Mendelian rules. Why it matters — potential implications for clinical genetics, disease risk, drug efficacy, sex-specific biology, and the relationship between nature and nurture.