Genetic information, variation and relationships between org

• Eukaryotic DNA


  • Longer
  • Linear
  • Associated with histones
• Prokaryotic DNA


  • Circular loops
  • Not associated with proteins
• Mitochondria and chloroplasts have their own circular DNA that is not wrapped around histones
• Gene


  Sequence of DNA that codes for a polypeptide or functional RNA
• Locus


  The exact position of a gene on a chromosome
• Genetic code


  • Degenerate
  • Universal
  • Non-overlapping
• Triplet


  A sequence of three bases on DNA that codes for an amino acid
• The genetic code has more than one triplet that codes for the same amino acid (degeneracy)
• The same triplet of bases codes for the same amino acid in all organisms (universality)
• Each base is only involved in one triplet (non-overlapping)
• Introns


  DNA sequences that do not code for polypeptides
• Exons


  DNA sequences that do code for amino acids
• Codon


  Three bases on mRNA that code for a specific amino acid
• Start codon


  Three bases that initiate translation
• Stop codon


  Three bases that terminate translation
• Genome


  An organism's complete set of genes
• Proteome


  The full range of proteins a cell can produce
• Bacterial genomes contain around 600,000 DNA base pairs, while human genomes contain 3 billion base pairs
• mRNA


  Single-stranded, shorter than DNA, found in cytoplasm and nucleus
• tRNA


  Has an amino acid binding site and an anticodon complementary to an mRNA codon
• Ribosome


  Holds tRNA molecules in place during translation
• Transcription


  1. DNA helix unwinds

  2. One DNA strand acts as template

  3. RNA nucleotides align to template

  4. RNA polymerase joins nucleotides

  5. Pre-mRNA is modified by splicing

  6. Mature mRNA leaves nucleus
• Translation


  1. mRNA binds to ribosome

  2. tRNA anticodons align to mRNA codons

  3. Amino acids are joined by peptide bonds

  4. Ribosome moves along mRNA

  5. Translation ends at stop codon
• Gene mutation


  A change in the DNA base sequence
• Gene mutations can have no impact if the new codon codes for the same amino acid
• Chromosome mutation


  Changes in the number of chromosomes
• Polyploidy


  Changes in the whole set of chromosomes (e.g. triploidy, tetraploidy)
• Aneuploidy


  Changes in the number of individual chromosomes (e.g. Down syndrome)
• Non-disjunction


  Chromosomes/chromatids fail to separate equally during meiosis
• Possible issues in Meiosis


  1. Non-disjunction occurs

  2. Gametes are haploid (n) or haploid plus/minus one chromosome (n+1, n-1)

  3. Trisomy (3 copies of a chromosome) can occur
• Meiosis


  • Two nuclear divisions, creates genetically different haploid gametes
  • Introduces genetic variation through independent segregation of homologous chromosomes and crossing over
• Identifying meiosis in life cycles


  Look for 2n to n transition
• Genetic diversity


  • Number of different alleles of genes in a population
  • Enables natural selection
• Natural selection


  1. New alleles created by random mutation

  2. Advantageous alleles more likely to be passed on

  3. Leads to evolution (change in allele frequency over generations)
• Types of natural selection

  • Directional selection (extreme traits selected for)
  • Stabilizing selection (middling traits selected for)
• Species


  • Organisms able to produce fertile offspring
  • Courtship behaviour is unique and essential for successful mating and reproduction
• Phylogenetic classification


  • Arranging groups according to evolutionary origins and relationships
  • Closer branching indicates more recent common ancestor
• Taxonomic hierarchy


  • Domain
  • Kingdom
  • Phylum
  • Class
  • Order
  • Family
  • Genus
  • Species
• Binomial nomenclature


  • Genus and species names
  • Universal system for identifying organisms
• Biodiversity


  • Variety of habitats, genes, and species in a community
  • Decrease in biodiversity is a concern, can be caused by human activities like farming