Fig. 7. Early pby1 stripes are of a two-segment periodicity. (A) The posterior portion of 18-20% grasshopper embryos stained for pby1 mRNA are shown. A1 and A2 pby1 stripes arise from within an initial A1/A2 broad domain, comprising the future pby1 stripes of A1 and A2. Note residual expression connecting A1 and A2 stripes during the individuation process (red arrow), as well as the low level of expression posterior to the A1 stripe through to the posterior tip. The individuation of stripes A1 and A2 is accompanied by the appearance of the A3/A4 broad domain, which will later refine into stripes A3 and A4. (B) The extending abdomens of 21-24% embryos immunostained for Pby (black) and En (brown) are shown. A5 and A6 Pby stripes arise from within the broad ‘A5/A6’ domain and A7 and A8 Pby stripes from within the broad ‘A7/A8’ domain. As in A, note the low level of expression throughout the posterior beginning from the most recently individuated anterior stripe. Also note that En stripes appear before the restriction of Pby stripes to the ventral neuroectoderm: the third embryo from the left shows both a restricted stripe (arrowhead, A2) with En and an unrestricted stripe (arrow, A3) posterior to which an En stripe is just beginning to appear. Although some broad domains appear after the previous (more anterior) broad domain has split (A), other broad domains appear before the anterior nascent stripes have fully individuated (B), though this may reflect a difference in the turnover rates of transcript versus protein. Scale bar: 100 µm. Embryos in A have swelled somewhat as a result of the in situ protocol.