Fig. 4. Schemetic representation of the serial homology in cell identity between OP sublineages and O and P sublineages. (A) Comparison of an op blast cell clone (top) and the paired o and p blast cell clones (bottom) during embryonic stage 7. At the stage shown, the op blast cell has undergone two rounds of division (see Fig. 1B), and the o and p blast cells have undergone their second cell division in only the anterior half of the clone. Each homologous pair of cells gives rise to the same set of pattern elements, and their nuclei are labeled here with the same color. The positional relationship between the OP, O and P sublineages is indicated with anterior to the top, ventral to the left and dorsal to the right. (B) Descendant pattern elements arising from one op blast cell, or a consegmental pair of o and p blast cells, in the stage 9 embryo. The clonal origin of the pattern elements is represented by the same color scheme used in Fig. 4A. See Fig. 3 for labeling of pattern elements.