Fig. 7. The expression domains of Drosophila and Tribolium gap genes. Head, thorax and abdomen are separated by vertical bars. (A) Fate map and gap gene expression in the Drosophila blastoderm. (B,C) Late blastoderm and early germ band stages in Tribolium (the photos to the right illustrate the stages represented by B and C). (B) In the Tribolium blastoderm only head and thoracic segments are specified. The posterior pole comprises the growth and patterning zone (growth z) and probably includes terminal cells (not shown). Extra-embryonic tissue has been omitted for simplicity. (C) During germ band growth, the posterior giant domain splits into stripes located in segments T3 and A2, far anterior of the segment primordia covered by Dm'giant (A). Although anterior expression domains of gap gene orthologs appear largely conserved (compare anterior domains of tailless, giant and hunchback), the posterior gap domains in Tribolium are shifted relative to the segment primordia. See discussion for further details.