Download Chapter 20: Classification of Living Things

Chapter 20: Classification of Living Things
Taxonomy (tasso - classify; nomos - usage)
This is a branch of biology concerned with identifying and naming organisms.
Aristotle - Greek philosopher - first to be interested in taxonomy
John Ray - British naturalist - organisms should have a set name.
Carolus Linnaeus - born Carl von Linne (Sweden) wrote “Species Planetarum” (1753). Developed
binomial nomenclature in which every organism has 2 names.
The Binomial System
Genus - more general, capitalized
Species - more specific, lower case
These are italicized or underlined. For example, Homo sapiens
specific epithet - usually describes the organism
Linnaeus - each species has its own unique characteristics not shared by members of a similar species.
Biological definition of a species - distinctive characteristics are passed from parents to offspring.
Members of the same species:
- interbreed
- share the same gene pool
This only applies to sexually reproducing organisms.
Some species vary widely, but still interbreed - leading to three-part names.
Subspecies - may actually be a distinct species.
Classification categories- assignment of organisms to categories on the basis of Phylogeny which is
evolutionary relationship.
Taxa - groups of organisms that fill a category
Aristotle - used 14 groups - mammals, birds, etc.
Ray - grouped animals and plants according to how he thought they were related.
Linnaeus - used physical characteristics to group.
Modern Groupings
Animal
Species
Genus
Family
Order
Class
Phylum * * * * * * * * * * * * * *
Kingdom
Plant
Species
Genus
Family
Order
Class
Division
Kingdom
“Kings Play Chess On Fine Green Sand”
Hierarchy - the higher the classification, the more inclusive.
Character - any feature (structural, chromosomal, molecular) that distinguishes one group from another.
Also - super, sub, infra for each category.
Systematics - study of diversity of organisms at all levels of organization.
Goal: to determine evolutionary history of a group of organisms.
Related species - share a common ancestor.
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Phylogenetic tree - a diagram that indicates common ancestors and lines of descent.
Primitive character - one that is present in the common ancestor and all members of the group.
Derived character - one that is found only in a particular line of descent.
Tracing Phylogeny
Fossil Record - sometimes difficult to interpret because the fossil record may be incomplete
Homology - possessing similar characteristics due to sharing a common ancestor.
Homologous structures - related through a common ancestor
Analogous structures - perform the same function but no common ancestor
Convergent evolution - development of similar characteristics on distantly related organisms.
Parallel evolution - related organisms share acquired characteristics; but common ancestor does not.
Molecular Data - Changes in an organism’s DNA can be used like a molecular clock.
May use different methods to test:
Protein comparisons – immunological differences, amino acid sequence differences
Ribosomal RNA - change slowly - bacteria
DNA-DNA hybridization - DNA from two species allowed to come together
Molecular clocks – use number of differences in DNA sequence to determine relatedness.
Systematics
3 Schools of systematics (study of diversity):
Traditional: stresses both common ancestry and degree of structural difference between divergent groups.
i.e.- high degree of evolutionary change - may not be grouped with common ancestor. (Birds and
mammals evolved from reptiles)
Cladist: stress common ancestry and derived characters only, discount adaptations to new environments.
i.e - birds are groups with reptiles.
Objective - species should be grouped by shared derived characteristics. e.g. - bat wings, whale
flippers
Numerical phenetics: species are clustered based on number of similarities. Measure total number of
traits, compare number that are similar, estimate degree of relatedness.
Classification Systems
From Aristotle’s time (300-400 BC) to 1880's, only kingdoms were Animalia and Plantae.
Upon the discovery and description of many microscopic organisms, a third kingdom was proposed,
Protista.
Protista was further divided into Lower protists and Higher protists:
Lower: prokaryotic - bacteria and cyanobacteria (blue-green algae)
Higher: divided into plant-like (included algae and fungi) and animal-like (included motile protists).
1969 - A five kingdom classification system was proposed by R.H. Whittaker:
Plantae, Animalia, Fungi, Protist, Monera
Three Domain System
Recent data suggest evolutionary Domains: Bacteria, Archaea, Eukarya
Bacteria – prokaryotic
Archaea – prokaryotics in extreme environments
Eukarya – eukaryotics; all remaining kingdoms
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