4.5 species and taxonomy

• what is a species

  a group of organisms that can (interbreed to) produce fertile offspring
• why 2 different species are unable to produce fertile offspring

  different species have different chromosome numbers → offspring may have odd chromosome number

  so homologous pairs cannot form → meiosis cannot occur to produce gametes
• why courtship behaviour is a necessary precursor to successful mating

  allows recognition of members of same species → so fertile offspring produced

  allows recognition / attraction of opposite sex

  stimulates / synchronises mating / production / release of gametes

  indicates sexual maturity / fertility

  establishes a pair bond to raise young
• phylogenetic classification system

  species (attempted to be) arranged into groups, called taxa, based on their evolutionary origins (common ancestors) and relationships

  uses a hierarchy ->

  smaller groups are placed within larger groups

  no overlap between groups
• taxa in the hierarchy of classification

  domain

  kingdom

  phylum

  class

  order

  family

  genus

  species
• how is each species universally identified

  a binomial consisting of the name of its genus and species

  eg homo sapiens
• advantage of binomial naming

  universal so no confusion as many organisms have more than one common name
• how can phylogenetic trees be interpreted

  branch point = common ancestor

  branch = evolutionary path

  if two species have a more recent common ancestor they are more closely related
• two advances that have helped to clarify evolutionary

  relationships between organisms

  advances in genome sequencing → allowing comparison of DNA base sequences

  more differences in DNA base sequences → more distantly related

  as mutations build up over time

  advances in immunology → allowing comparison of protein tertiary structure

  higher amount of protein from one species binds to antibody against the same protein from another species → more closely related

  as indicates a similar amino acid sequence and tertiary structure

  so less time for mutations to build up