The linear sequence specification of a gene product is not provided by the target DNA sequence alone but by the mechanisms of gene expressions. The main actors of these mechanisms, proteins and functional RNAs, relay environmental information to the genome with important consequences to sequence selection and processing. This 'postgenomic' reality has implications for our understandings of development not as predetermined by genes but as an epigenetic process. Critics of genetic determinism have long argued that the activity of 'genes' and hence their contribution to the phenotype depends on intra- and extraorganismal 'environmental' elements. As will be shown here, even the mere physical existence of a 'gene' is dependent on its phenotypic context.