Certain of their generalized features make chromosomes the ideal discursive transition from the basically genetic to the basically environmental aspects of cancer. On the one hand, chromosomes display certain relatively constant, essentially genetically- determined features. Among the latter are the streamlining of chromosomes in prokaryotes in contrast with their redundancy and higher-ordered packaging in eukaryotes; their species-specific shape, size, number, and banding pattern; and their individual- specific combinations of relatively common phylogenetically and mitotically stable subunits contained in specific gene pools. On the other hand there are variable features, many of which can be induced by suitable environmental agents. Among these are features reflected in meiotic nondisjunctions giving rise to monosomies and trisomies of whole chromosomes; and in chromatid breakages which may or may not be viable, be repaired, be repaired faithfully, or be followed by aberrations such as fragmentations, deletions, duplications, exchanges, translocations, and ring formations. Indeed, it was the observations of some of these chromosomal instabilities that led Boveri, significantly during the year the First World War started, to propose his somatic mutation hypothesis of tumorigenesis.
KeywordsGeneral Principle Chromosome Anomaly Ataxia Telangiectasia Pericentric Inversion Ring Chromosome
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