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Ch_16_lacOperon - Chapter 11.4-11.6 Transposable Elements...

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Chapter 11.4-11.6: Transposable Elements
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Class I: DNA transposons Transpose as DNA (replicative or non-replicative) Encodes transposase, which necessary for movement Found in bacteria, as well as eukaryotes e.g. IS1 ( E.coli ), AcDs (maize), P elements ( Drosophila ) Class II: Retrotransposons RNA is copied into DNA by reverse transcriptase (often coded by the transposon itself) and inserted back into the genome Found only in eukaryotes e.g. Ty (yeast), Gret1 (grapes), Alu elements in humans Classes of TEs
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DNA RNA Proteins transcription translation replication RNA replication ribozymes retrotransposons DNA transposons
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Class I: P elements in Drosophila P+ x P- P- does not produce a repressor No repressor in the egg cytoplasm Sperm do not donate a repressor When the P element enters the cytoplasm, there is no repressor present and there is a burst of transposition hybrid dysgenesis mutant / sterile offspring
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Ac element produces transposase Which stimulates transposition of Ds into color (C) gene producing yellow kernels Ds eaves the C gene, it restore pigmentation in some cells (a sector) Size of sector depends on when the excision of Ds took place (early vs. late in development Class I: Ac & Ds in maize
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A geneticist examines an ear of corn. Most kernels are yellow but a few have purple spots. Give an explanation for the yellow kernels. Give an explanation for the presence of purple spots. Order the kernels below in terms of when the gene was ‘turned on’. Yellow kernels are due to the transposition of a Ds element into the color gene. Purple dots are due to the transposition of a Ds element out of the color gene during development. 3 1 4 2
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Class II: Retrotransposons in Grapes Black and red grapes result from production of red pigments – anthocyanins Gret1 transposon inserted in the promoter region of the vvmybA1 gene shutting down pigmentation production, producing white grapes The removal of part of the retrotransposon (through faulty recombination) restored partial pigmentation production resulting in red grapes black white red promoter
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Chapter 16: Gene Expression in Bacteria
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