3.4.5

• Species

  If two organisms belong to the same species they are able to produce fertile offspring

  • Offspring from 2 different species mating may be infertile because they will have an odd number of chromosomes so can’t perform meiosis to produce (haploid) sex cells (gametes)
• Courtship behaviour is a necessary precursor to successful mating. The role of courtship in species recognition.

  Allows recognition of members of the same species because courtship behaviour is species specific

  Production of fertile offspring

  Indication of sexual maturity

  Recognition/attraction of opposite sex

  Stimulate release of gametes

  Establishes a pair bond to raise young

  • Synchronise mating → maximum probability that sperm will fertilise ovum
• A phylogenetic classification system

  Arranges species into groups based on their evolutionary origins (common ancestors) and relationships

  What is a hierarchy

  Smaller groups placed within larger groups

  No overlap between each group

  • Each group = taxon
• One hierarchy comprises the taxa:

  Domain (drunken)

  Kingdom (kangaroos)

  Phylum (punch)

  Class (children)

  Order (on)

  Family (family)

  Genus (game)

  • Species (shows)
• Each species is universally identified by a binomial consisting of the name of its genus and species

  Genus e.g. homo + Species e.g. sapien

  = Homo sapien

  • Advantage – universal; no confusion as many organisms have more than one common name
• Students should be able to appreciate that advances in immunology and genome sequencing help to clarify evolutionary relationships between organisms

  Genome sequencing

  Compare the order of base sequence of whole genome of different species

  • Higher % match = more closely related e.g. humans and chimps = 96%
• Immunology

  DNA → mRNA → sequence of amino acids in polypeptide

  So tertiary structure of protein tells us about sequence of DNA

  • If same antibody binds to a specific antigen then it is closely related