Summary

The next question to solve was "How do genes make a whole organism grow back out of a single cell?" (185). A geneticist named Ed Lewis began to study fruit flies to determine things like "how does a fly embryo 'know' to grow a leg out of the second thoracic segment or an antenna out of its head (and not vice versa)?" (186). Lewis concluded that "the building of organs and structures [...] is encoded by master-regulatory 'effector' genes that work like autonomous units or subroutines" (187). In a series of papers published between 1986 and 1990, a scientist named Nusslein-Volhard and her colleagues explored this topic further, identifying the following process: "Proteins in the early embryo are deposited preferentially at one end by the mother. They activate and silence genes, thereby defining the embryo's axis from head to tail. These genes, in turn, activate...