How mutations occurs in virus
Answers
Answer:
by the change in the DNA coding...or change in genetic material coding
Answer:
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Explanation:
Viruses are continuously changing as a result of genetic selection. They undergo subtle genetic changes through mutation and major genetic changes through recombination. Mutation occurs when an error is incorporated in the viral genome. Recombination occurs when coinfecting viruses exchange genetic information, creating a novel virus.
Mutations
Mutation Rates and Outcomes
The mutation rates of DNA viruses approximate those of eukaryotic cells, yielding in theory one mutant virus in several hundred to many thousand genome copies. RNA viruses have much higher mutation rates, perhaps one mutation per virus genome copy. Mutations can be deleterious, neutral, or occasionally favorable. Only mutations that do not interfere with essential virus functions can persist in a virus population.
Phenotypic Variation by Mutations
Mutations can produce viruses with new antigenic determinants. The appearance of an antigenically novel virus through mutation is called antigenic drift. Antigenically altered viruses may be able to cause disease in previously resistant or immune hosts.
Vaccine Strains from Mutations
Mutations can produce viruses with a reduced pathogenicity, altered host range, or altered target cell specificity but with intact antigenicity. Such viruses can sometimes be used as vaccine strains.
Recombination
mutation, called antigenic drift, may allow a virus to outflank host defenses and cause disease in previously immune individuals.
Figure 43-1. Mutation causing phenotypic (antigenic) variation.
Figure 43-1
Mutation causing phenotypic (antigenic) variation. . Mutation of the codon for the hydrophilic amino acid serine to the codon for the hydrophobic amino acid phenylalanine can change an epitope on the viral hemagglutinin protein and thereby alter its recognition (more...)
Vaccine Strains from Mutations
Mutation has been a principal tool of virologists in developing attenuated live virus vaccines (Table 43-1). For example, the Sabin vaccine strains of poliovirus were developed by growing polioviruses in monkey kidney cells. Mutation and selection produced variant polioviruses that were adapted for efficient replication in these cells. Some of the mutations in these variants affected the genes coding for the poliovirus coat proteins in such a way as to produce mutants unable to attach to human neural cells but still able to infect human intestinal cells. Infection of human intestinal cells does not produce paralytic disease but does induce immunity. Poliovirus vaccine strains 1 and 2 have multiple mutations in the coat proteins and are very stable. The type 3 vaccine strain is less stable and is subject to back-mutations (reversions) that restore neural virulence. This vaccine strain therefore causes paralytic disease in one out of every several million vaccinated individuals. Despite the possibility of back-mutations, the generation and selection of attenuated viral mutants remains an important mechanism for producing viral vaccines.