Species + 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 of opposite sex

  ● Stimulates mating + release of gametes

  ● Indicates fertility

  ● Establishes a pair bond to raise young
• Describe a phylogenetic classification system

  ● Species arranged into groups, called taxa, based

  on their 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

  (Largest) Domain → 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
• Describe 2 advances that have helped to clarify evolutionary

  relationships between organisms

  1 Advances in genome sequencing → allow comparison of DNA base sequences

  ● More differences in DNA bs → more distantly related ancestor

  ● As mutations build up over time

  2. Advances in immunology → allowing comparison of protein tertiary structure

  ● Higher amount of protein from 1 species binds to antibody against the same protein from another species → more closely related ancestor

  ● As indicates a similar amino acid sequence and tertiary structure

  ● So less time for mutations to build up