Figure 2.

Classification of epialleles based on potential influence of genetic sequences. Pure epialleles shift between transmissible chromatin states (chromatin modification [m]) with no change in genetic sequence at linked or unlinked genomic positions. In other cases, a genetic change, such as a transposable element (TE) insertion or structural variant (SV), can produce directed chromatin changes, resulting in an obligatory allele. Alternatively, the genetic change can result in a poised allele that can exist in two potential chromatin states (facilitated).