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.