3.7+3.8 sequences

• Natural selection


  variation present in (original population); individuals with an advantageous characteristic/allele more likely to survive; (these reproduce and) pass on genes offspring; increase (in frequency) of advantageous alleles;
• Speciation


  reproductively isolated / no interbreeding; conditions different for two populations / different selection pressures; different features or plants are selected or survive / different adaptations; populations become (genetically) different / unable to produce fertile offspring;
• Random sampling

  – quadrats


  Principle of randomly placed quadrats and method of producing random quadrats (e.g.two tape measures at right angles to create a grid over the area – random number generator to give coordinates to place quadrat); Valid method of obtaining no. dandelions in given area (e.g.mean per quadrat / total no. in many quadrats); Multiply to give estimate for total field area;
• Systematic

  sampling –

  quadrats in

  transects

  Quadrats placed at intervals along transect; Number of organisms counted per quadrat to calculate organisms per m2; Large number/sample of quadrats; Divide total percentage by number of quadrats; Measure named variable (e.g. light intensity) at each site; Spearman’s rank to determine if there is a correlation
• Mark release

  recapture


  Capture / collect / sample, mark and release; Leave time for organisms to disperse before second sampling; Population = number in first sample × number in second sample divided by number of marked in second sample / number recaptured;
• Succession

  Colonisation by pioneer species; Pioneers change the named environment/habitat/conditions/factors; Environment becomes less hostile for new species Change/increase in diversity/biodiversity;

  To climax community;
• Different kinds of mutations

  • Change in the base/nucleotide
  • No effect because: Genetic code is degenerate (so amino acid sequence may not change)
  • No effect because: Mutation is in an intron (so amino acid sequence may not change)
  • Does change amino acid but no effect on tertiary structure
  • New allele is recessive so does not influence phenotype
  • Has positive effect because: Results in change in polypeptide that positively changes the properties (of the protein)
  • Has positive effect because: Results in change in polypeptide that positively changes a named protein
  • Has positive effect because: May result in increased reproductive success or may result in increased survival (chances)
• Results in the formation of new allele


  Change in the base/nucleotide
• How transcription

  factors control

  transcription


  a protein complementary to promotor region of a specific gene Binds to gene Interacts with RNA polymerase to either promote binding / prevent binding Increase/decrease rate of transcription
• RNAi


  siRNA binds to / destroys mRNA Prevents translation of protein Protein synthesis reduced
• Epigenetic control of gene expression

  Methylation and acetylation
• Methylation


  • Methyl groups (CH3) can be added to a carbon molecule on cytosine bases within sequences that contain multiple cytosine and guanine bases
  • Addition of methyl groups (methylation) suppresses the transcription of the affected gene because the methylated bases attract proteins that bind to the DNA and inhibit transcription
• Acetylation


  • Acetyl groups (COCH3) can be added to lysine amino acids on histone proteins
  • Lysine has a positively charged R group, this forms ionic bonds with the negatively charged phosphate backbone of DNA
  • Adding acetyl (acetylation) to lysine residues removes the positive ion and therefore removes a bond between the histone protein and the DNA
  • This causes the DNA to be less tightly wrapped
  • When the DNA is less tightly wrapped, RNA polymerase and transcription factors can more easily bind and therefore gene expression is stimulated
• In vivo cloning

  (making

  recombinant DNA,

  transforming cells,

  identifying

  transformed cells)

  Restriction endonucleases/enzymes cuts plasmid; produces ‘sticky ends’; Same restriction enzyme to cut gene of interest; Ligase joins gene/DNA and plasmid; Bacteria transformed; Plasmid contains two markers; One marker prevented from being expressed by the insertion of the gene of interest; Identify bacteria that have taken up the modified plasmid by the presence of the marker proteins; Allow genetically modified bacteria to reproduce.
• In vitro cloning

  (PCR)

  Heat DNA; Breaks hydrogen bonds / separates strands; Add primers; Add nucleotides; Cool; (to allow) binding of nucleotides / primers; DNA polymerase; Role of (DNA) polymerase; Repeat cycle many times;
• Producing DNA

  fingerprints (PCR,

  gel

  electrophoresis)

  DNA is cut; Using restriction enzyme; Use electrophoresis; Separates according to length / mass; Southern blotting / transfer to (nylon) membrane; Make single-stranded; Apply probe; Radioactive / fluorescent; Reference to tandem repeats / VNTRs / minisatellites; Autoradiography if using a radioactive probe