3.4.4

• Genetic diversity is the number of different alleles of a gene in a population.
• Variation of alleles exists in a population due to random DNA mutations, for example, some bacteria contain a gene for antibiotic resistance due to a mutation.
• Selection pressure or change in the environment, such as the introduction of an antibiotic, can lead to the survival and reproduction of those with advantageous alleles, resulting in differential survival and reproductive success.
• Bacteria with a gene for resistance survive and reproduce, while those without it die.
• Those surviving or reproducing pass the advantageous allele to their offspring.
• The frequency of the advantageous allele and the named characteristic increases in the population over many generations or a long period of time, a process known as evolution: change in allele frequency over time.
• Directional selection e.g. antibiotic resistance in bacteria

  • Change to the environment
  • Selection pressure acts one side of the mean
  • One extreme phenotype more likely to survive and produce
  • Bacteria with gene for antibiotic resistance
  • Mean phenotype changes

  
• Stabilising selection e.g. human birth weights :

  • Stable environment
  • Selection pressure acts either side of the mean
  • Both extremes of phenotype less likely to survive and reproduce
  • Very small or very large babies
  • Mean phenotype remains the same

  
• Natural selection results in better adapted species|

  • These adaptations all increase an organism's chance of survival (and/or reproduction)
  • Anatomical
  • Structural features of organisms body / observed structures
  • E.g. whales thick layer of blubber helps keep warm in cold sea
  • PhysiologicalProcesses inside the body
  • E.g. brown bears hibernate in the winter, lower metabolism to conserve energy so they don't need to look for food when its scarce
  • Behavioural
  • Ways an organism acts
  • E.g. possum plays dead if they're being threatened by a predator, to escape attack
• Species

  itsering trims belorent steisman is the are til teauce fertil eavesdd number

  of chromosomes so can't perform meiosis to produce (haploid) sex cells (gametes)

  Example exam question

  The red panda is native to South East Asia. There are two populations that are separated by a deep river gorge. These populations are very different from each other in appearance.

  How could scientists show that the two populations are the same species? (2 marks)

  Breed together red pandas from different areas

  If fertile offspring, then still same species
• 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 (didn’t )

  Kingdom (know)

  Phylum (poop)

  Class (Could)

  Order (Occur)

  Family (fabulously)

  Genus (golden)

  Species (shaped)
• 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
• RELATIONSHIPS:

  • 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