Classification

Classification

1. Phylogenetic Classificaion

   • Reflecting evolutionary relateness
   • Phylogenetic tree
     • Diagram showing evolutionary descent
       • Living organisms at the top of the branches
         • Ancestral species in the branches & trunks
           • Branch points represent common ancestors
             • The further up you go, the further up in time
               • Species in the branches are extinct

2. Classification is hierarchal

   • Hierarchal= A system of ranking in which small groups are components of larger groups
     • Moving down the Hierarchy organisms in a taxon are more closely related
       • Each grouping in a system is called a Taxon
         • Taxon = Any group within a system of classification
           • Taxa are discrete
             • I.e They can only belong in 1 taxon & no other
             • E.g This picture
               • Exoskeleton & jointed limbs are the same
                 • As well as the same No. of limbs
                   • But have different No. of wings, which places them in different taxa
   • Hierarchy of biological classification
     • Domain
       • Kingdom
         • Phylum
           • Class
             • Order
               • Family
                 • Genus
                   • Species

3. Purpose of a classification system

   • Lets us infer evolutionary relationships
     • E.g if 2 organisms are very similar we put them in the same taxon
       • We infer that they are closely related
   • Easier for communication
     • E.g it's easier to say 'Bird' than 'vertebrate egg-laying biped with feathers & beak'
   • When describing the health of an ecosystem/rate of extinction
     • It is more useful to refer to families than species

4. The 3 domain system

   • The largest taxon
     • Defined on basis of DNA & rRNA sequences
       • Domains
         • Eubacteria
           • Normal Bacteria
         • Archaea
           • Extreme Bacteria
         • Eukaryota
           • Animals, Plants, Fungi, Protoctista

5. The 5 Kingdom System

   • Prokaryotes
     • Prokaryota
   • Eukaryotes
     • Animalia
     • Plantae
     • Fungi
     • Protoctista

6. Species

   • A group of organisms that can interbreed to produce fertile offspring

7. Relatedness of organisms

   • Theory of evolution suggests that all species have a common ancestor
   • Assessing relatedness w/physical features
     • When looking at how closely-related 2 species are
       • Biologists look for homologous structures
         • Homologous Structures
           • Similar structure of component to perform a different function
             • May have similar developmental origin
           • E.g Pentadactyl Limb
             • Limb w/5 digits
               • But adapted for different functions
             • Divergent Evolution
               • Where a common ancestral structure has evolved & performs different functions
               • Analogous strucutures
                 • Have corresponding function & similar shape
                   • But different origin
   • Assessing relatedness w/genetic evidence
     • DNA sequences
       • During course of evolution species undergo changes in their DNA base sequences
         • Which eventually accumulate until organisms become different species
           • The more closely related a species the more similarity in their DNA sequences
             • DNA analysis confirms/ corrects evolutionary relationships
     • DNA hybridisation
       • Comparing DNA base sequences of 2 species
         • To work out how closely related 2 species are:
           • 1) DNA is extracted & fragmented
             • Fragments are mixed together
               • Complementary base sequences hybridise
                 • This gives a percentage
     • Amino acid sequences
       • Sequence of amino acids are determined by the sequence of DNA
         • The degree of similarity in the amino acid sequence of same proteins reflects how closely related they are
     • Immunology
       • Proteins of different species can be compared using immunological techniques
         • If antigens of one species is mixed w/specific antibodies of another
           • The antigens & antibodies make a precipitate
             • The closer the evolutionary relationship the more precipitate is made

8. The species concept

   • The Morphological definition
     • If 2 organisms look very similar they are likely to be of the same species
       • Morphology = The literal shape/form of the organism
   • The Reproductive definition
     • If 2 organisms are of the same species
       • They can interbreed to produce fertile offspring

9. The Binomial System

   • Naming system given to organisms of all species
     • Made up of Genus name & Species name
   • The names are unambiguous & can be understood worldwide
     • Regardless of language spoken
   • How to use the binomial system
     • Genus name is 1st & 1st letter is capital
       • Species name is 2nd & all lowercase
         • Both name written in italics & underlined

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