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Chapter 10

Chapter 10 - Genetic Recombination.docx

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Athabasca University
BIOL 204
Dr.Roland Treu

CHAPTER 10 GENETIC RECOMBINATIONUltimate source of genetic diversity is mutation of DNA sequence often resulting from errors during DNA replicationoMutations relatively rare TF diversity t various mechanismsgenetic recombinationGenetic recombinationoLiterally cuttingpasting DNA backbones into new combosoAllows jumping genes to move inserts some viruses into chromo of their hosts underlies spread of antibiotic resistance among bacteria and is at heart of meiosis in euks101 Mechanism of Genetic RecombinationIn most general sense reqs12 DNA mol that differ from oneanother in at least 2 places2Mechanism for bringing DNA mol into close proximity3Collection of enzymes to cut exchange and paste DNA back tghMost recombination occurs btwn regions of DNAverybut not identical in sequence of basesoRegionshomologousoShort as few base pairs or as long as entirechromoOnce homologous DNA regions paired enzymes break covalent bond in each backbone free ends of each backbone exchanged and reattached to those of other DNA molResult 2 recombined mol in which original red nowcovalently bonded to other blue DNAvv102 Genetic Recombination in BacteriaHistorically first assocd w meiosis in sexuallyreproducing euksProksoMechanisms to bring DNA from diffcells tgh and tht this DNA recombinesto create offspring diff from either parent celloIn some types of bacterial recombinationone of participating cells is dead102a Genetic Recombination Occurs in E coliLederbergTatum expmtto test whether bacteria had a kind of sexuality in their reproduction processE coli and many other bacteria can be grown in minimal medium containing water an organic carbon source eg glucose and a selection of inorganic salts including one such as ammonium chloride tht provides nitrogenoCan be liquidgel form gel add agar to liquidCloneslarge cultures of genetically identical cells to study oTo create spread over sterile agar gel in culture dishoCulture diluted enough to ensure cells will be widely separated on agar surfaceoEach cell divides many times to produce clump of identical cells called a colonyTo detect genetic recombination need detectable differences shown to occur in changing combosoDiff most useful related to nutritioncells req various AAs for synthesis of proteinsoStrains able to synth necessary AAs called prototrophsoMutant strains unable to synth AAs called auxotrophscan only grow if reqd AA provided in growth mediumoStrain tht cannot manufacture own arginineargGene tht governs cells ability to synth arginine from simple inorganic mol where normalargAlt forms of gene called alleles and might differ by as little as one base pair in DNA sequenceUsing mutagens eg Xrays or UV light they isolated 2 diff strains of E coli carrying distinctive combos of alleles oIsolated using replica plating where transferring of cells from complete media to minimal medium media where auxotrophs fail to growoThey mixed c100M cells of 2 mutant strains tgh and placed them on minimal mediumSeveral hundred colonies grew even though indvly none of original cells carried all of normal alleles needed for growthTF some form of recombination btwn DNA mol of 2 parental types must have produced necessary combo w normal alleles for each gene102b Bacterial Conjugation Brings DNA of Two Cells into Close ProximityBacterial cells first thought to bring DNA tgh by fusingoLater transfer of genetic info is unidirectional conjugate instead of fusing tht is cells contact each other by long tubular structure called sex pilus and then form cytoplasmic bridgeDuring conjugation copy of part of DNA of one cell moves t cytoplasmic bridge into other celloOnce DNA from once cell enters other genetic recombination can occur
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