There are three fundamental types of genes that give way to the developmental structure of the fly: maternal effect genes, segmentation genes, and homeotic genes.
It has been suggested that the thrifty phenotype is the consequence of three unlike adaptive processes: maternal effects, niche construction and developmental plasticity, which all are influenced by the brain.
Their expression patterns in the early embryo are determined by the maternal effect gene products and shown in the diagrams on the right side of this page.