Medical brain notes 33

  Taxonomic systems   The initiation for eolving taxonomic systems was provided by  Aristotle  (384 - 322 BC) . He emphasized that animals can be classified according to their way of living, actions, habits and body parts. He observed insects, fishes, birds and whales. The insect orders like Coleoptera, Diptera were created by him. Due to his contributions, he is considered as the '  father   of biological classification '.   For modern taxonomy, the first work was carried out by  John Ray  (1627 - 1705) of England. His most interesting systematic work '  Synopsis   Methodica Animalium Quadrupedum et Serpentini Generis ' was published   in 1693. He divided animals into those with blood and those without blood. He also classified animals based on gills, lungs, claws, teeth and other structures. He provided the first good definition of the species as 'a reproducing unit'.   The great Swedish naturalist  Linnaeus  (Caroli Linnaei) (1707 - 1778) exerted an important

  Introduction to taxa and species   While grouping or arranging the organisms, a biologist faces three scientific ideas, namely taxonomy, systematics and classification. These disciplines though appear similar have slight deviations in their meaning.   The term  taxonomy  is a Greek word. Its components are  taxis  and  nomos . While   taxis   means arrangement,   nomos   means law. Thus taxonomy   is defined as the ' theory and practice of classifying organisms ' (E. Mayr 1966). The term  systematics  originates from the Greek word  systema . It means 'placing together'. Thus systematics means classification of living things in accordance with their natural relationships. G.G Simpson (1961) defines systematics as follows '  Systematics is the scientific study of the kinds   and diversity of organisms and of any and all relationships among them '.   The term  classification  in meaning partly overlaps with taxonomy. However it simply means the activity of class

  Methods of taxonomy Phenetic method or Numerical taxonomy   This method involves clustering or grouping of individuals of a taxon or several taxa. Based on overall similarity, identifications are being made. The desired size of the clusters or groupings is called the  operational   taxonomic unit  (OTU).   The identification method involves measurement of taxon to taxon simi-larity or dissimilarity. It is measured using a scale of 0 to 1. '1'represents perfect identity. '-1'designates dissimilarity between taxa. In this method enormous amount of data are collected for related groups. Analyses are made, using statistical tools and computers.   Cytotaxonomy   The characterization and identification of a cell's complete  chromosome  set is referred to as  karyotyping . It is the first stage in the  process of using chromosomes in taxonomy.   Karyotypes within interbreeding populations of a species are usually constant. Between species there may be variation in chromo

  Nomenclature methods   Nomenclature forms the basis by which scientists can name and cross refer to organisms. It is an integral part of taxonomy. In fact, modern tax-onomy started in 1753 with the publication of first part of  Systema  by  Linnaeus . According to Linnaeus a Species is specified by the combination of both its specific and generic names. Since it requires two names, it is referred to as the  binomial system . This system is now firmly established in Biology.   In modern times International Commissions are responsible for nam-ing each major group of organisms. There are several such commissions. These commissions authorize the usage of scientific names in biology. Naming of animals is monitored by  International Code of Zoological Nomenclature  (ICZN) (International Commission of Zoological Nomenclature, 1985).   The rules are set out in the 'codes'. The codes are modified by occasional science congresses. Basic principles of nomenclature   1.    Providing  sta