Fig. 1.

Transgenerational inheritance systems. a Offspring inherit from their parents genes (black), the environment (green) and culture (blue). Genes and the environment affect the epigenome (magenta) and the phenotype²². Culture also affects the phenotype, but at present there is no evidence for a direct effect of culture on the epigenome (broken blue lines). It is a matter of debate, how much epigenetic information is inherited through the germline (broken magenta lines). G genetic variant, E epigenetic variant. b An epimutation (promoter methylation and silencing of gene B in this example) often results from aberrant read-through transcription from a mutant neighboring gene, either in sense orientation as shown here or in antisense orientation. The presence of such a secondary epimutation in several generations of a family mimics transgenerational epigenetic inheritance, although it in fact represents genetic inheritance. Black arrow, transcription; black vertical bar, transcription termination signal; broken arrow, read-through transcription