classification, taxonomy, and nomenclature Flashcards
how are living things ‘classified’ today?
into 3 domains: bacteria, archaea, and eukarya
what was the first attempt to classify viruses?
Homes tried to use the Linnaean hierarchical system:
- order: Virales
- Group 1: Phaginae (viruses that infect bacteria)
- Group 2: phytophaginae (viruses that infect plants)
- Group 3: Zoophaginae (viruses that infect animals)
prior to 1930 how were viruses classified?
based on the disease and symptoms, however this is not accurate:
- ex. for Hepatitis A (Picornaviridae), Hep B (Hepadnaviridae), and Hep C (Flaviviridae), they’re all caused by different virus families
- ex. for mosaic viruses of plants, they also belong to different families
how were viruses classified from 1930-1966?
- based more now on the virus over the disease it can cause
- more based on morphology, capsid structure, chemical composition and genome type
- all viruses were then classified into groups if they shared the same morphology, capsid structure, chemical composition and genome type
how are viruses classified now (1966-present)?
ICTV classifies viruses as a “monophyletic group of viruses whose properties can be distinguished from those of other species by multiple criteria”
- monophyletic = members of the group come from the same ancestor
what is monothetic classification (suggested by ICTV)?
viral classification/grouping based on one characteristic at a time (ie. genome, capsid structure, naked or enveloped)
- doesn’t work because it assumes all members of a group originate from the same ancestor
what is the definition of taxonomy?
the science of naming, classifying, and defining groups of organisms based off of shared characteristics
what is polythetic classification (suggested by ICTV)?
viral classification/grouping based on shared characteristics, but not all are shared
- works because doesn’t assume that all members of a group evolved from the same ancestor
in practice, how are viruses defined/organized?
by their relatedness in sequences (nucleotide and amino acid sequences) in a specific gene or set of genes (capsid protein genes, helicase genes, etc)
what are the rules (grammar?) for naming viruses?
- name is italicized
- 1st letter of name is capitalized
- 1st letter of place names are also capitalized (ex. West Nile)
- acronym of a virus name does NOT need to be italicized
how are bacterial, plant, insect, and vertebrate viruses named?
- bacterial viruses: based on specific coding (ex. T-2 bacteriophage)
- plant viruses: host virus was first discovered in + symptom (ex. Tobacco mosaic virus)
- insect viruses: latin name of host + effects of infection
- vertebrate viruses: disease & symptoms (ex. hepatitis viruses)
what makes up a taxon?
order, family, (subfamily), genus, and species Ex: order: picornaVIRALES family: picornaVIRIDAE genus: enteroVIRUS species: polioVIRUS
what are the characteristics used to define a genus/family?
- nature and organization of viral genomes (ss/ds, DNA/RNA, pos/neg, segmented/non-segmented)
- virion morphology and architecture of capsid (symmetry, shape and size, and enveloped or naked)
- genome replication strategies
- number and size of structural & non-structural proteins
- enzymes (polymerases, etc)
what are the characteristics used to define a species?
- host range in nature
- cell and tissue tropism (ie. hepatitis affects liver cells)
- pathology (in host) and cytopathology (in cell culture)
- mode of transmission (biological vectors, air-borne, etc)
- physio-chemical properties (ex. inactivation temp)
- antigenic properties of viral proteins
- sequence relatedness of genes & genomes
what is phylogeny?
the prediction of evolutionary relatedness among viruses based on comparison of their sequences
