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Genetische Variatie - Coggle Diagram

- - - - Arise without exposure to external agents, may result from errors in DNA replications
        
        Base tautomerization resulting in transition and transversion mutations
        
        Insertion or deletion of nucleotides
      - May also result from action of mobile genetic element such as transposons
    - - Alternative (and controversial) hypothesis: proposed that some bacteria can select which mutations occur so they can better adapt to their environment
        
        Explanation may be that hypermutation occurs: the random generation of multiple mutations with only those cells containing the favorable mutations able to survive
    - - Caused by agents that directly damage DNA
        
        Base analogs: mistake when they are incorporated not growing polynucleotide chain
        
        DNA modifying agents: alter a base causing it to mispair
        
        Intercalating agents: distort DNA to induce single nucleotide pair insertions and deletions
        
        UV damage of DNA result in formation of thymine dimers resulting in DNA that can no longer serve as a template
  - - - Morphological mutations
      - Lethal Mutations
      - Conditional mutations: expressed only under certain environmental conditions
      - Biochemical mutations
        
        Auxotrophic mutant: unable to make an essential macromolecule like an amino acid or nucleotide
        
        Wild-type strain from which it arose is called a prototroph
        
        Resistant mutant
        
        resistent tegen een bepaalde stof
  - - - Silent mutation: change nucleoside sequence of codon but not the encoded amino acid
      - Missense mutation: single base substitution that changes codon for one amino acid into codon for another amino acid
      - Nonsense mutation: converts a sense codon to a stop codon
      - Frameshift mutation: results from insertion or deletion of one or 2 base pairs in the coding region of the gene
  - - - Observation of changes in phenotype
      - Replica plating technique
        
        used to detect auxotrophic mutants (kan iets niet meer aanmaken)
      - Mutant selection
        
        Use of environmental condition in which only desired mutant will grow
        
        Carcinogenicity Testing
        
        based on observation that most carcinogens are also mutagens
        
        tests for mutagenicity are used as screen for carcinogenic potential
        
        e.g., Ames test
- - - - nucleotide excision repair
      - base excision repair
  - - - used to directly repair thymine dimers
    - - catalyzed by alkyltransferase or methylguanine methyltransferase
  - - - used to distinguish old DNA strands from new DNA strands: Old DNA are methylated
      - catalyzed by DNA methyltransferases
- - - - Direct cell to cell contact mediated by the F pilus (buis)
      - A type IV secretion system
    - - a copy of the F factor is transferred to the recipient and does not integrate into the host chromosome
      - Donot genes usually not transferred
    - - donor HFr cell has F factor integrated into its chromosome
      - donor genes are transferred to recipient cell
      - a complete copy of the F factor is usually not transferred
    - - result when the F factor incorrectly leaves the host chromosome
      - some of the F factor is left behind in the host chromosome
      - some host genes have been removed along with some of the F factor
        
        these genes can be transferred to a second host cell by conjugation
      - F' x F- Mating
  - - - bv vaak in water, bodem, biofilms
      - In de natuur vaak => lineaire DNA-fragmenten
      - In het labo meestal circulaire DNA-fragmenten
  - - - any part of bacterial genome can be transferred
      - Occurs during lytic cyle
      - during viral assembly, fragments of host DNA mistakenly packaged into phage head (limited capacity)
        
        Generalized transducing particle
    - - Ofwel integratie genen -> doorgeven aan dochtercellen
      - Ofwel geen integratie, wel expressie:
        
        abortieve transductanten
    - - carried out only by temperate phages that have established lysogeny
      - only specific portion of bacterial genome is transferred
      - occurs when prophage is incorrectly excised
        
        Defectieve faag
        
        meestal in bezit van enkele bacteriële genen maar niet meer in staat tot vervullen volledige virale cyclus = “transducerend partikel”
        
        LFT lysaat
        
        slechts klein deel van de fagen na lyse van de cellen zal een transducerend partikel zijn
- - - - Hfr x F- mating interrupted at various intervals
      - order and timing of gene transfer determined
    - - Gene locations expressed in minutes, reflecting time transferred
      - made using numerous Hfr strains
- - - - Exogenote
        
        DNA that is transferred to recipient
      - Endogenote
        
        genome of recipient
      - Merozygote
        
        recipient cell that is temporarily diploid as result of transfer process
    - - homologous recombination
        
        Double-Strand Break Model
        
        Nonreciprocal HR
        
        incorporation of single strand of DNA into chromosome, forming a stretch of heteroduplex DNA
        
        proposed to occur during bacterial transformation
      - site specific recombination
        
        important in insertion of viral genome into host chromosomes
        
        there is only a small region of homology between inserted genetic material and host chromosome
      - transposition
        
        segments of DNA that move about the genome in a process called transposition
        
        can be integrated into different sites in the chromosome
        
        are sometimes called “jumping genes”
        
        the simplest transposable elements are insertion sequences
        
        transposable elements which contain genes other than those used for transposition are called composite transposonss
        
        Types of transposable elements
        
        Replicative transposition