Virus Genetics

This document provides a summary of genetic mechanisms which operate in viruses and some of the practical implications which arise from these.

It is possible to separate molecular analysis of virus genomes into two types of approach:

Physical analysis of structure and nucleotide sequence, essentially performed in vitro.
Biological analysis of the structure-function relationships of intact virus genomes and individual genetic elements usually involving analysis of the virus phenotype in vivo.

Conventional genetic analysis of animal viruses is based on the isolation and analysis of mutants, using plaque-purification techniques. For viruses which do not form plaques, little genetic analysis was possible before the development of molecular genetics, but certain tricks make it possible to use these genetic techniques for such viruses, e.g:

Focal immunoassays
Biochemical analysis
Physical analysis
Molecular biology
Formation of transformed 'foci' of cells.

Types of genetic map:

Recombination Maps
Reassortment Maps/Groups
Physical Maps
Restriction Maps
Transcription Maps
Translation Maps

Virus Mutants:

'Strain', 'type', 'variant', 'mutant' and even 'isolate' are all terms used interchangably to differentiate them from original 'parental', 'wild-type' or 'street' viruses.

Spontaneous mutations
Induced mutations

Types of Mutation:

Plaque morphology
Host range
Temperature-sensitive (t.s.)
Cold-sensitive
Nonsense
Deletions
Biochemical markers
Revertants

Genetic Interactions Between Viruses:

Recombination
Reassortment
Complementation

There are two possible types of complementation:

Allelic (intragenic) complementation: where different mutants have complementing defects in the same protein
Non-allelic (intergenic) complementation: resulting from mutants with defects in different genes

Non-Genetic Interactions Between Viruses

Heterozygosis
interference
Suppression
Phenotypic mixing
Pseudotyping

Genome Evolution

Genetic and nucleotide sequence relationships between viruses can reveal the origins of not only individual viruses, but of whole families and possible virus 'superfamilies':

Detailed notes for these documents can be found in Chapter 3 of Principles of Molecular Virology.

Standard Version: The 4th edition contains new material on virus structure, virus evolution, zoonoses, bushmeat, SARS and bioterrorism, CD-ROM with FLASH animations, virtual interactive tutorials and experiments, self-assessment questions, useful online resources, along with the glossary, classification of subcellular infectious agents and history of virology. (Amazon.co.uk)

Instructors Version: The 4th edition contains new material on virus structure, virus evolution, zoonoses, bushmeat, SARS and bioterrorism, CD-ROM with all the Standard Version content plus all the figures from the book in electronic form and a PowerPoint slide set with complete lecture notes to aid in course preparation. (Amazon.co.uk)

Detailed notes for these documents can be found in Chapter 3 of Principles of Molecular Virology.
Standard Version: The 4th edition contains new material on virus structure, virus evolution, zoonoses, bushmeat, SARS and bioterrorism, CD-ROM with FLASH animations, virtual interactive tutorials and experiments, self-assessment questions, useful online resources, along with the glossary, classification of subcellular infectious agents and history of virology. (Amazon.co.uk)	Instructors Version: The 4th edition contains new material on virus structure, virus evolution, zoonoses, bushmeat, SARS and bioterrorism, CD-ROM with all the Standard Version content plus all the figures from the book in electronic form and a PowerPoint slide set with complete lecture notes to aid in course preparation. (Amazon.co.uk)