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.”
Read more about this topic: Genetic Determinism
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