Classification

Phylogenetic Classificaion
1. Reflecting evolutionary relateness
2. Phylogenetic tree
  1. Diagram showing evolutionary descent
    1. Living organisms at the top of the branches
      1. 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
Classification is hierarchal
1. Hierarchal= A system of ranking in which small groups are components of larger groups
  1. Moving down the Hierarchy organisms in a taxon are more closely related
    1. Each grouping in a system is called a Taxon
      1. 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
2. Hierarchy of biological classification
  1. Domain
    1. Kingdom
      1. Phylum
        Class
        Order
        Family
        Genus
        Species
Purpose of a classification system
1. Lets us infer evolutionary relationships
  1. E.g if 2 organisms are very similar we put them in the same taxon
    1. We infer that they are closely related
2. Easier for communication
  1. E.g it's easier to say 'Bird' than 'vertebrate egg-laying biped with feathers & beak'
3. When describing the health of an ecosystem/rate of extinction
  1. It is more useful to refer to families than species
The 3 domain system
1. The largest taxon
  1. Defined on basis of DNA & rRNA sequences
2. Domains
  1. Eubacteria
    1. Normal Bacteria
  2. Archaea
    1. Extreme Bacteria
  3. Eukaryota
    1. Animals, Plants, Fungi, Protoctista
The 5 Kingdom System
1. Prokaryotes
  1. Prokaryota
2. Eukaryotes
  1. Animalia
  2. Plantae
  3. Fungi
  4. Protoctista
Species
1. A group of organisms that can interbreed to produce fertile offspring
Relatedness of organisms
1. Theory of evolution suggests that all species have a common ancestor
2. Assessing relatedness w/physical features
  1. When looking at how closely-related 2 species are
    1. Biologists look for homologous structures
      1. 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
3. Assessing relatedness w/genetic evidence
  1. DNA sequences
    1. During course of evolution species undergo changes in their DNA base sequences
      1. 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
  2. DNA hybridisation
    1. Comparing DNA base sequences of 2 species
      1. 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
  3. Amino acid sequences
    1. Sequence of amino acids are determined by the sequence of DNA
      1. The degree of similarity in the amino acid sequence of same proteins reflects how closely related they are
  4. Immunology
    1. Proteins of different species can be compared using immunological techniques
      1. 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
The species concept
1. The Morphological definition
  1. If 2 organisms look very similar they are likely to be of the same species
    1. Morphology = The literal shape/form of the organism
2. The Reproductive definition
  1. If 2 organisms are of the same species
    1. They can interbreed to produce fertile offspring
The Binomial System
1. Naming system given to organisms of all species
  1. Made up of Genus name & Species name
2. The names are unambiguous & can be understood worldwide
  1. Regardless of language spoken
3. How to use the binomial system
  1. Genus name is 1st & 1st letter is capital
    1. Species name is 2nd & all lowercase
      1. Both name written in italics & underlined

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