Shared Developmental Processes Plant cells don’t move; they change the orientation of cell division. Animal cells move: in gastrulation, cells in different parts of an early embryo rearrange themselves into three distinctive types of embryonic tissues
Regulatory Genes Form Cascades The interactions among bicoid and the segmentation genes form a regulatory cascade. Master regulators trigger the production of other regulatory signals and transcription factors, which trigger production of another set of signals and regulatory proteins, and so on. The bicoid gene, gap genes, pair-rule genes, segment polarity genes, and homeotic genes each define a level in the cascade.
Developmental Pathways and Evolutionary Change Once biologists began working out regulatory signals and cascades, they realized that the genetic changes altering these developmental processes must be the foundation of evolutionary change. Evo-devo is the research field of evolutionary-developmental biology. It focuses on understanding how changes in developmentally important genes have led to the evolution of new phenotypes.