4.5 Species and taxonomy

• What is a species?

  A group of organisms that can (interbreed to) produce fertile offspring
• Suggest 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
• Explain 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
• Describe a 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
• Name the taxa in the hierarchy of classification

  Domain (largest / broadest) → kingdom → phylum → class → order → family → genus → species (smallest)
• How is each species universally identified?

  A binomial consisting of the name of its genus and species, eg. Homo sapiens
• Suggest an 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 (eg. C & D)

  
• Describe two advances that have helped to clarify evolutionary relationships between organisms (genome sequencing)

  1. Advances in genome sequencing → allowing comparison of DNA base sequences
  2. ● More differences in DNA base sequences → more distantly related / earlier common ancestor
  3. ● As mutations (change in DNA base sequences) build up over time
• Describe two advances that have helped to clarify evolutionary relationships between organisms (immunology)

  1. Advances in immunology → allowing comparison of protein tertiary structure (eg. albumin)
  2. ● Higher amount of protein from one species binds to antibody against the same protein from another species → more closely related / more recent common ancestor
  3. ● As indicates a similar amino acid sequence and tertiary structure
  4. ● So less time for mutations to build up