RELIABLE SEGMENTATION BY SUCCESSIVE BIFURCATION

In many organisms, a reliable number of segments is produced even thou gh important properties of the region involved, especially its size at the time of pattern formation, are apparently not specified with suff icient precision. We show that this can be readily accomplished if seg mentation occurs through a sequence of bifurcations rather than all at once, and we provide evidence from developmental studies that indicat es that this is typically what actually occurs. Our results strongly s uggest that where patterns are formed reliably, this generally happens in stages rather than by the setting up in advance of a complete prep attern.