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Genetics Lectures 27-29.doc

24 Pages

Biology (Sci)
Course Code
BIOL 202
Tamara Western

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Lecture 27Genetics of Transposable Elementsunstable alleles of maizeBarbara McClintockLoss of a piece of a choromsome Called Ds locus for disocciator between centromere and DsRequired presence of unlinked Activator Ac locus Ds locus only broke when Activator was present as well on the chromosome at a different locus AcactivatedDs were jumping to the colour locus to give the color spots and then leave again Mobile elements but only in the presence of Ac also a jumping geneHybrid Dysgenesis of DrosophilaCrossed wild isolate males x lab strain females F1 progeny were sterilechromosome breakage made unstablemutations in germ line Unstable mutations of white eyes with red spots from dysgenic crossEcoliEnlarged mutant alleles in Unstable lacgal mutants of E coli found to contain extra DNADid a density gradient and found 2 bands Normaland large mutant allelesFirst evidence was that these unstable alleles were caused by something moving into the genes and coming out again Could find the same sequence in the large gal allele at multiple times in the chromosome In Ecoli there were several mobile elements making it unstable This was the evidence of the mobile genetic elements What is happening Loss of protein function due to insertion of large piece of DNA intocoding regionoTE inserting into the regulatory region losing colour because losing transcription factor that regulation colour productionInsertions also can result in changes in gene expression if lands in a regulatory region or if transcription of gene now driven by transposable element regulatory sequencesoCan also overactivate the gene or activate it at the wrong time if the promoter region is affectedGetting a base white flower because the TE currently in the pigmentation gene is knocking out the pigment gene Can have restoration of the colour when the TE removed itself early so you have large coloured spots These are called revertant sectorsCells where the TE transposed out of the gene later in development multiply into small revertant coloured sectors Stable mutations caused by TE when they are not able to cleave themselves out cleanlyCould have mutation or deletion of portions of the TE required for recognition by transposase such that the TE is immobilized Or knock out the function of the transposase gene only if one transposase to start withError in transposition leading to imprecise excision leaving a couple base pairs behind This is more likely to happen than one transposase Transposon footprints that could knock out the function of something Fate of progeny depends on whether somatic or germline eventTE insertions or movements that occur in somatic cells are nonheritableTE insertions or movements that occur in germline cells will be passed on to progenyTE insertions or movements that occur in germline cells will be passed on to stable mutant progeny This most likely could be due to imprecise transposition of a transposable element
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