Lecture 3 Flashcards
What is taxonomy?
“In the end, all nature is a continuum, and the business of taxonomy has the unfortunate obligation of drawing boundaries within this continuum, an artificial and illogical east, but necessary nevertheless”
Explain the Linnaeus classification system
In the 1700s, which classified plants and animals
What is the classification system used today?
It is the three domain system, which classifies bacteria, archaea, and eukarya
What is the Homes legacy?
Homes attempted to adopt the Linnaean system to classify and name viruses: failed
What did Homes attempt to do?
Homes classified the order virales:
Group I: Phagine (viruses that infect bacteria)
Group II: Phytophaginae (viruses that infect plants)
Group III: Zoophaginae (viruses that infect animals
Faced strong criticism and was rejected
Explain how the hepatitis virus was classified
Hepatitis virus causes different types of hepatitis:
1) Hep A: Hep A virus, family Picornaviridae
2) Hep B: Hep B virus, family Hepadnaviridae
3) Hep C: Hep C virus, family Flaviviridae
These 3 are entirely different viruses
Explain how the mosaic viruses are classified
1) TMV –> family Virgaviridae
2) Cauliflower mosaic virus –> family Caulimoviridae
3) Cucumber mosaic virus –> family Bromoviridae
4) Turnip yellow mosaic virus –> family Tymoviridae
What is the difference between virus and disease?
Viruses are the living organisms and agents that causes an infection or disease
Diseases are the final outcome and manifestation of an infection resulting from interactions between a virus and its host
Infection can lead to disease, but does not necessarily cause disease
What happened in the later days with taxonomy?
There was more emphasis on virus over disease
Viruses was based on morphology, capsid structure, chemical composition, and type go genome. All viruses were classified into groups
In the later days with taxonomy, how were viruses classified into ‘groups’?
1) Herpesvirus group: dsDNA, icosahedral capsids, large virion size, enveloped
2) Poxvirus group: dsDNA, complex & irregular virion structure, 200 nm or larger, enveloped
3) Myxovirus group: (-)ssRNA, helical nucleocapsids, spherical virion, enveloped
What happened with classification in the modern days?
In 1966, the International Committee on the Taxonomy of Viruses was established. Two approaches were considered: Monthetic and polythetic
What is the monothetic approach being considered by the ICTV?
Based on one characteristic at a time: the nature of viral genome (nucleic acid), capsid symmetry, presence or absence of envelope. The issue however is that this assumes all members in a group originated from the same and only one ancestor, and this is unable to capture and reflect the vast diversity of viruses
What is the polythetic approach being considered by the ICTV?
This considers multiple properties and characteristics. Individual viruses in a group share most, but not all, of a set of common characteristics, this does not assume that all viruses in a group evolved from a common ancestor
This ultimately how viruses were classified.
What is the older definition of a virus?
A polythetic class of viruses that constitute a replicating lineage and occupy a particular ecological niche
What is the new definition of a virus?
A monophyletic group of viruses whose properties can be distinguished from those of other species by multiple criteria
