 The next experimental milestone for theories of genetic control of development was Christiane Nüsslein-Volhard and collaborators’ painstaking characterization of mechanisms of body patterning and polarity in Drosophila (e.g., Driever &amp; Nüsslein-Volhard 1988). They distinguished three regions along the early embryo’s anteroposterior body axis (anterior, posterior, and terminal), the basic patterns and structures of which are controlled by distinct sets of maternal genes. A few such genes have long-range “organizing” effects. Notably, Driever and Nüsslein-Volhard (1988) showed that bicoid protein acts as a morphogen, controlling formation of a fly’s anterior (including head and thorax) in accordance with its concentration gradient. Significantly, their experimental manipulations were DNA sequence mutations (known to effect anterior body plan development or bicoid copy number). The experiments thereby charted a causal pathway from DNA to mRNA to protein to cell differentiation to morphogenesis. This demonstration of changes in body-plan correlated with maternal genetic mutations was powerful vindication of the idea that genes control development. Moreover, central concepts of the organicist alternative (gradients and positional information) were brought under the rubric of that theory. Nüsslein-Volhard’s gene-based approach remains influential in developmental biology (see the entry on  developmental biology).