The stately progression of cell division in an early embryo is familiar to us from video footage used in countless biology classes. But this image does not portray the importance of cell location and movement. The embryo could divide indefinitely, but without spatial information it would remain an undifferentiated blob. Something must break the symmetry to enable development of a front end, a back end, and everything in between. Some species use an environmental cue (gravity), some use a physical cue (sperm entry point) but, more commonly, they use a chemical cue to initiate asymmetry and form axes of differentiation.Spatial information is particularly important for cells that migrate during embryo development. In Drosophila eggs, the nuclei divide, but no cell walls form, producing a syncitium (polynucleate cell) that persists for the first few hours of embryogenesis. The nuclei migrate to the periphery of the embryo, where cell walls grow around them. How do the cells know where to go? Chemical cues have been identified that guide cells to their destination (and indeed can attract cells in the wrong direction if mis-expressed). A new gene has been identified in Drosophila that produces a germ cell guidance signal, active in the earliest stages of embryogenesis [1xSlow as molasses is required for polarized membrane growth and germ cell migration in Drosophila. Stein, J.A. et al. Development. 2002; 129: 3925–3934PubMedSee all References[1]. When this new gene is missing, germ cells fail to traverse the embryo to reach the developing gonad in time, and are left in the midgut (so, although the unfortunate mutants survive to wriggle around as larvae, they presumably never have offspring of their own). This is not because the germ cells themselves are deficient, but because of the lack of a guidance system that tells them where to go. Similar to other early embryonic signalling genes, this gene is expressed both maternally and zygotically. It is also responsible for cellularization, which turns the syncytial bag of nuclei into a multicellular embryo.Counter to common sense, new genes are not named for what they do, but for what happens when they are not expressed. Because of the slow progress of germ cells in these mutants, this gene has been named slow as molasses (slam). Development has been the missing link in evolutionary biology, the ‘black box’ between genotype and phenotype, but new techniques are uncovering developmental processes at such an astounding rate that it is almost impossible to keep up with new discoveries. The penchant of developmental biologists to give novel genes slightly silly names might simply reflect a field where discovering a new gene has become an almost daily activity. At least if you call a gene makes caterpillars floppy (mcf), there is no doubt about what it does [2xSee all References[2].