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Variable expressivity and epigenetics

Part 1. Genetics

1.3. Epigenetics

Short Specialist Review

  1. Marnie E. Blewitt,
  2. Emma Whitelaw

Published Online: 15 JUL 2005

DOI: 10.1002/047001153X.g103324

Encyclopedia of Genetics, Genomics, Proteomics and Bioinformatics

Encyclopedia of Genetics, Genomics, Proteomics and Bioinformatics

How to Cite

Blewitt, M. E. and Whitelaw, E. 2005. Variable expressivity and epigenetics. Encyclopedia of Genetics, Genomics, Proteomics and Bioinformatics. 1:1.3:36.

Author Information

  1. University of Sydney, Sydney, Australia

Publication History

  1. Published Online: 15 JUL 2005


There is an increasing awareness that some genes do not behave in a strictly Mendelian fashion. In plants, flies, and mice, some alleles have been identified where the activity state varies among cells of the same cell type (termed variegation) and among genetically identical individuals (variable expressivity). We now know that this is the result of the stochastic establishment of differential epigenetic states at the locus. These states are set up during early development and are stably inherited for the life of the organism. While, in general, the states are cleared between generations, this is not always the case. Some alleles, now referred to as metastable epialleles, are not completely cleared from one generation to the next, resulting in a phenomenon termed transgenerational epigenetic inheritance. One of the interesting questions that arises from these findings is whether this mechanism has been involved in the evolution of morphological traits.


  • variegation;
  • variable expressivity;
  • epigenetics;
  • parent-of-origin effect;
  • epigenetic inheritance;
  • mouse