Fig. 2

Expression of the pair rule genes opa (a-a’), slp (b-b′) and h (c-c’) in embryos at early and late abdominal segmentation. Throughout development, opa (a, a’) is expressed in a narrow band at the border of every segment but is not found in the posterior GZ. slp (b, b′) is more broadly and anteriorly expressed in each segment. The earliest, most posterior stripes are thin, and increase in breadth anteriorly. In later stages (b’), it shows diffuse expression in the limb buds. h expression (c-c′) is similar to that of opa in nascent segments but is weaker in mature segments. In the anterior GZ it is expressed in two stripes at the anterior of the anterior GZ, and more weakly in the posterior GZ. There is also weak punctate expression in the limb buds. Embryo ages are as in Fig. 1. In all images, anterior is to the top