Segmentation is well understood in Drosophila, a long germ insect in which all the segments are specified in the blastoderm. But most insects develop as short germ embryos and follow the ancestral mode of segmentation in which only the anterior segments are specified in the blastoderm. On , Bucher and Klingler investigate segmentation in the flour beetle Tribolium castaneum, a short germ insect, by examining the expression and function of the gap gene giant. While the anterior domain of giantexpression is similar in both insects, the posterior domain of Tc'giant expression is much more anterior than that of Dm'giant. The function of giant also differs between the two insects. For example, Tc'giant has a long-range effect on abdominal patterning, whereas Dm'giant functions only in its limited expression domain. The researchers suggest that changes in the abdominal gap gene system are central to the evolution from short to long germ insects.
