Figure 2. Evo-devo models offer many routes to explore patterning and morphogenesis.

(A) In butterflies, colors can be formed using pigments, such as the ommochrome pigment (orange), which works by absorbing all wavelengths of light except orange. In contrast, structural colors are formed by reflection of light interacting with components of the scale to selectively reflect blue wavelengths in the optix knockout. The structure of the scale is quite complex consisting of a lower lamina (LL) connected to an upper lamina composed of ridges (R), microribs (MR), and crossribs (CR). (B-C) Differences in rodent molar morphology. (B) In a cross-sectional view of the mouse molar, cusps are separated, but in gerbils cusps are connected by a ridge called a loph. (C) Occlusal view of an adult tooth with cusps represented by circles. Cusps can either be parallel or alternate in their placement on the tooth. (D) Morphology of the dorsal appendage (arrowhead) of the Drosophila eggshell differs in placement and number between species. Early morphogenesis of these homologous structures also differ, with the dorsal appendage of D. melanogaster forming through neighbor exchange events (red cells) and the dorsal appendage of S. lebanonensis (also known as S. pattersoni) forming through cell shape changes (red cells).