Position Effects and Genetic Code in Relation to Epigenetic Systems

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Abstract
Recent discussions of genetic and epigenetic systems pertain to the central biological problem of heritable control over development and function of organisms. Distinguishing between genetic and epigenetic phenomena involves difficulties due to their mutual characteristics. Epigenetic systems, if controlling the action of genetic systems, nevertheless, must be genetically persistent. However, genetic systems also have an epigenetic aspect concerned with the physiology of their own reproduction, distinct from the physiology of their heterocatalytic function.[long dash]- Epigenetics re-emphasizes a basic distinction between genotype and phenotype, between stored information and the expression of information. Confusion results if this primary concept is violated by subsequent restricting definitions. Thus, in addition to code sequence of nucleotides, other chromosomal differentiations having hereditary persistence are likely. Demonstrated position effects imply a code of genotypic significance residing in higher level chromosomal organization. Therefore, our concept of a genetic system storing information should not be restricted to the denotation of "gene" or to limited aspects of DNA structure. It is preferable to retain the broader connotation of hereditary persistence for a genetic system. We would then recognize more than one type of genetic code and several classes of genetic change.[long dash]- Interactions among genetic systems, their products, and their cellular environment have epigenetic or developmental significance, but may also result in alteration of certain types of genetic code. Biochemical and biophysical refinements of description may be superposed upon this complex of interacting systems, using terminology such as has been suggested by Lederberg.
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