Methylation of cytosine bases encodes epigenetic information that governs lineage-specific patterns of gene expression. Remodelling the methylated genome accompanies major transitions during embryo development, including fertilisation, blastulation and gastrulation. The first whole genome epigenetic maps of this modification across these embryonic transitions in a metazoan has been reported in the zebrafish, and shows surprising differences from the long-accepted models developed from more limited analyses of mammalian embryos. The analysis of the zebrafish shows a primacy of the sperm's epigenome as a blueprint for creating the embryonic epigenome. The study illustrates the strengths of comparative approaches to complex biological questions.

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