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Epigenetic phenomena

Epigenetic phenomena are the "X-files" of biology - unusual events that cannot be explained by Mendel's rules of genetics and which often cannot be predicted. Broadly defined, epigenetic phenomena are heritable (or propagated), alternative states of gene expression, molecular function, or organization specified by the same genetic instructions (DNA sequence).

Examples include:

  • the unpredictable "on" or "off" expression patterns of wild-type (non-mutant) genes in certain chromosomal contexts. This is especially evident among genes after a chromosome rearrangement has occurred (e.g. position effect variegation), among genetically engineered genes (transgenes), and among repetitive genes or duplicated genes, especially if they are arranged in inverted orientation.
  • alternative states of protein folding that can be propagated from one protein molecule to the next. Examples include prions of neurodegenerative disorders such as bovine spongiform encephalopathy (BSE, or "mad cow disease"), Kuru, or Creutzfeldt-Jakob Disease.
  • alternative, self-perpetuating developmental patterns. An example is the alternate choice of cilia orientation in Paramecium.

Nucleolar dominance, involving the silencing of rRNA genes transcribed by RNA polymerase I, RNA-directed DNA methylation, and siRNA-mediated effects on nucleus organization are phenomena currently being studied in the Pikaard lab.