epigenetic programming of gene expression epigenetic programming in the zygotic pronuclei chromatin reprogramming in the zygote Reactome:R-HSA-9821993 2012-10-24T13:53:28Z GO:0044725 Reactome:R-HSA-9821002 biological_process jl The global programming of epigenetic modifications in the zygote following fertilization. The paternal genome undergoes active DNA demethylation before the first cell division, while the adjacent maternal genome is protected from this process.