Fertilization triggers a complex cellular programme that transforms two highly specialized meiotic germ cells, the oocyte and the sperm, into a totipotent mitotic embryo: linkages between sister chromatids are remodelled to support the switch from reductional meiotic to equational mitotic divisions; the centrosome, which is absent from the egg, needs to be reintroduced; the axis of cell division is shifted from extremely asymmetric to symmetric; genomic imprinting is selectively erased and re-established; and protein expression shifts from translational control back to transcriptional control. Recent work has started to reveal how this remarkable transition from meiosis to mitosis is achieved.
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