Genetics 389
Genetics
&Justasinhigherlifeforms,viralgeneticmaterialissubjecttochangeby
mutation.Lackofacorrectivereplication“proofreading”mechanismresults
inaveryhighincidenceofspontaneousmutationsinRNAviruses,inturn
greatlyincreasingthegenotypicvariabilitywithineachspecies(“viralqua-
sispecies”).Furthermore,apotentialforrecombinationofgeneticmaterialis
alsoinherentinthereplicationprocess,notonlymaterialfromdifferent
virusesbutalsofromhostcellandvirus.Thisfactorplaysamajorrolein
viraltumorinductionandgeneticengineering.Functionalmodifications
arisingfrominteractionsbetweendifferentviralspeciesinmixedinfec-
tions—e.g.,phenotypemixing,interference,andcomplementation—have
nothingtodowithgeneticchanges. &
Lastinggeneticchangesinvirusesarecaused,asinthehigherlifeforms,
eitherbymutationorrecombinationofgeneticmaterial.Temporarynonge-
neticinteractionsbetweenvirusesinsomecasesmaymimicgeneticchanges.
ReleaseofRetrovirusesfromanInfectedCell
Fig. 7. 6 Electron micro-
scopeimageofreleaseof
viralprogeny.Theprocess
takesplaceintheorder,
A,B,C.
7
Kayser, Medical Microbiology © 2005 Thieme