Fig. 1. An embryonic time course of transcript profiles based on precise staging of small cohorts of embryos. (A) Nucleus count versus minutes after the first cleavage at 22°C for all of embryogenesis (adapted, with permission, from Sulston et al., 1983). The area in green indicates the time domain covered by the time course. (B) The time points and the estimated average number of cells per time point in the time course. Embryos were staged at pseudocleavage and the four-cell stage as indicated. Samples for time points in blue and yellow were created, processed and assayed as independent time courses — series 1 and series 2. (C) The complete lineage through the 190-cell stage with the assayed time points indicated. The names given to each time point reflect how the embryos were staged and how long they were aged before being frozen (PC6, pseudocleavage plus 6 minutes; 0 min, four-cell stage plus 0 minutes).