1 Microbial genetics (Ch. 7) Part 3 -- Creating genetic diversity Types of mutations Mutagens Transduction Conjugation Transformation Transposons

2 Types of mutations (Fig. 7.22) Mutations are changes in the sequence of the genome Point mutations are changes in only one basepair (bp) AT-> GC, transition AT-> CG, TA, transversion

3 Mutagens (Fig. 7.22, 7.23) UV light causes pyrimidine dimers Chemical mutagens are analogs of normal bases or cause a chemical change that causes misreplication of DNA

4 Frameshift mutagens (Fig. 7.24) Frequently mutagens like ethidium bromide intercalate into DNA and cause DNAP to insert or delete bases

5 Horizontal gene transfer among prokaryotes via transformation Horizontal genetic transfers occurs within a population of the same generation (vs. vertical) Typically occurs with only 1% of a population Occurs cross-species and cross-genera, i.e., can pass genes to unrelated organisms Transformation, transduction and conjugation all cause horizontal gene transfer Many factors that contribute to pathogenesis may be transferred via these processes

6 Transformation (Fig. 7.30) Recipient cells (competent) take up DNA from environment and incorporate pieces into the chromosome Some pathogens (Haemophilus, Neisseria, Streptococcus, Bacillus, Staphylococcus) are naturally competent Competent cells can be artificially produced by injuring cell membranes (Biotechnology)

7 Transduction (Fig. 7.31) Carried out by bacteriophage that sometimes package the host’s DNA by mistake Phage also can transduce genes when they insert themselves into the chromosome and later pop out with attached host DNA

8 Bacterial conjugation (Fig. 7.32) Depends on specialized plasmids (F) that can transfer themselves from one cell into another (often unrelated genetically) via F pilus Some transfer themselves to eukaryotic cells (Ti plasmid, R751) Some R plasmids also transfer antibiotic resistance genes

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10 Transposons (Fig. 7.35) Jumping genes first discovered by Barbara McClintock in corn Transposons are mobile genetic elements that carry a gene that carries out the transposition and may carry other jeans as well Transposons can be carried by plasmids or phage

11 Transposon structure (Brock, Fig )

12 Mechanism of transposition (Fig. 7.36) Many of these sequences carry drug resistance genes and many drug resistant plasmids carry several transposons