Mutation is seen in -

Ans. is 'b' i.e.. Influenza virus o A unique feature of the influenza virus is its ability to undergo antigenic variations.o Antigenic variability is highest in influenza virus Type A and less in Type B, while it has not been demonstrated in type C.o Surface antigens hemagglutinin and neurominidase, undergo independent antigenic variations which may be of Two types.Antigenic drifto Antigenic change is gradual over a period of timeo The new antigens, though different from the previous antigens, are yet related to them,o Antigenic drift involves point mutation in the gene owing to selection pressure by immunity in the host population.o Antigenic drift accounts for the periodic epidemics of influenza.o Occurs every 2-3 years in case of Influenza A and every 4-7 years in case of Influenza-BAntigenic shifto An abrupt, drastic, discontinuous variation in the antigenic structure,o Result from genetic recombination of human with animal or avian virus,o Accounts for the major epidemics or pandemics,o Occurs every 10-15 years,o Occurs in influenza 'A' only