THE CLASSIFICATION OF LIVING ORGANISMS   Taxonomy or Systematics:   The study of classification   ODWS  Paul Billiet 2011
Why classify organisms?   <ul><li>Over a million species so far identified </li></ul><ul><li>Estimates of up to 30 million...
The unit of taxonomy:   The SPECIES <ul><li>The term species has biological significance </li></ul><ul><li>Species form po...
How taxonomy works <ul><li>The aim is to group organisms according to their evolutionary relationship ( phylogeny ) </li><...
Comparing phenotypes & genotypes <ul><li>Taxonomists compare a new specimen with given characteristics:  </li></ul><ul><li...
Hierarchy of characters <ul><li>Taxonomy uses many different characteristics to define a taxon </li></ul><ul><li>One chara...
Example <ul><li>So having four legs with five toes is common to all land vertebrates and their fish ancestor </li></ul><ul...
The pentadactyl limb <ul><li>Classification led to comparisons of shape and form that gave rise to comparative anatomy </l...
The pendadactyle limb Lizard Human Frog Bat
Analogous or homologous characters <ul><li>Even though the front legs of different mammals may look different they still u...
Homology in mammalian fore limbs ODWS  Paul Billiet 2011
Analogous structures <ul><li>Some structures may look very similar but have evolved independently </li></ul><ul><li>They a...
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Taxonomy

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Taxonomy

  1. 1. THE CLASSIFICATION OF LIVING ORGANISMS Taxonomy or Systematics: The study of classification ODWS Paul Billiet 2011
  2. 2. Why classify organisms? <ul><li>Over a million species so far identified </li></ul><ul><li>Estimates of up to 30 million species on Earth </li></ul><ul><li>Need to organise this biodiversity </li></ul><ul><li>Systematics tells us about the patterns in nature, the way organisms are related and how they evolve </li></ul><ul><li>Systematics can be used to identify organisms that are important to us </li></ul>ODWS Paul Billiet 2011
  3. 3. The unit of taxonomy: The SPECIES <ul><li>The term species has biological significance </li></ul><ul><li>Species form populations of individuals which may interbreed to form fully fertile offspring </li></ul><ul><li>Problem: Some species only use asexual reproduction or rarely use sexual reproduction </li></ul>ODWS Paul Billiet 2011
  4. 4. How taxonomy works <ul><li>The aim is to group organisms according to their evolutionary relationship ( phylogeny ) </li></ul><ul><li>Established by studying the phenotypes of living organisms or fossils </li></ul><ul><li>More recently DNA sequencing permits the comparisons of the genotypes </li></ul><ul><li>Uses characteristic features to group organisms together (e.g. all animals with feathers = Birds) </li></ul><ul><li>Taxonomists decide which are the most significant or &quot;important&quot; characteristic by the way it occurs in different groups of organisms. </li></ul>ODWS Paul Billiet 2011
  5. 5. Comparing phenotypes & genotypes <ul><li>Taxonomists compare a new specimen with given characteristics: </li></ul><ul><li>morphology </li></ul><ul><li>anatomy </li></ul><ul><li>behaviour </li></ul><ul><li>embryology </li></ul><ul><li>protein structure </li></ul><ul><li>karyotypes </li></ul><ul><li>DNA sequence (DNA fingerprints) </li></ul>ODWS Paul Billiet 2011
  6. 6. Hierarchy of characters <ul><li>Taxonomy uses many different characteristics to define a taxon </li></ul><ul><li>One character is not enough </li></ul><ul><li>The characteristics are grouped in a hierarchy. </li></ul>ODWS Paul Billiet 2011
  7. 7. Example <ul><li>So having four legs with five toes is common to all land vertebrates and their fish ancestor </li></ul><ul><li>This would be used to group the animals we call tetrapods </li></ul><ul><li>Having a nerve cord running down the back is a feature common to all the tetrapods but also all the rest of the vertebrates </li></ul><ul><li>So it can be used to group all the vertebrates but not the tetrapods alone. </li></ul>ODWS Paul Billiet 2011 Acanthostega Lamprey
  8. 8. The pentadactyl limb <ul><li>Classification led to comparisons of shape and form that gave rise to comparative anatomy </li></ul><ul><li>Comparative anatomists noticed that different species have similar structures used for different functions (e.g. the pentadactyle limb of terrestrial vertebrates) </li></ul><ul><li>These are called homologous structures. </li></ul>ODWS Paul Billiet 2011
  9. 9. The pendadactyle limb Lizard Human Frog Bat
  10. 10. Analogous or homologous characters <ul><li>Even though the front legs of different mammals may look different they still use the same bones in their structure </li></ul><ul><li>The simplest explanation for this is that they all originated from a common ancestor, the ancestor of all mammals </li></ul><ul><li>This is called homology </li></ul><ul><li>As organisms evolved they split up and specialised in different ways of living </li></ul><ul><li>Their bodies changed in shape but they still retain some of their ancestors features </li></ul>ODWS Paul Billiet 2011
  11. 11. Homology in mammalian fore limbs ODWS Paul Billiet 2011
  12. 12. Analogous structures <ul><li>Some structures may look very similar but have evolved independently </li></ul><ul><li>They are the product of natural selection on an organ adapting an organism to a particular niche </li></ul>ODWS Paul Billiet 2011 Thylacine Thylacinus cynocephalus Wolf Canis lupus

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