Medical Microbiology

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