Genetic Determinism - The Contemporary View

The Contemporary View

Despite surprises about the quantity and distribution of genes, genetic determinism remains the standard model. According to Nusslein-Volhard, who won a Nobel for her research into molecular mechanisms of development, the genome is a "building plan," DNA a "language of four letters that can be read faultlessly... In the fertilized egg, the genetic program is complete." She reiterates the reductionist approach even as she fleshes out a model of development based not on genetic information but the way genes are “expressed.” She notes that it's rare that one gene determines a specific structure in a specific position. Rather than provide anything like a blueprint for the finished organism, homeobox genes guide development by regulating other genes.

A given organic form is thought to emerge at a particular place in the embryo on the basis of its distance from an "organizer," a set of cells that influence how other cells develop. By generating a chemical gradient that permeates the embryo, the organizer establishes zones of development. Depending on which zone a cell is located in, some of its genes are expressed while others are repressed. “Through an interplay of mutual activation and repression, more and more complex molecular patterns emerge.”