GEN 3022 1st Edition Lecture 31 Outline of Last Lecture I Gene conversion a Example I b Gap repair synthesis vs DNA mismatch repair II Transposition a Cut and paste mechanism b Reverse transcriptase III Homologous Recombination a Holliday model b Recombinant and nonrecombinant chromosomes c Heteroduplex DNA Outline of Current Lecture I Modes of transposition a Simple transposition b Retrotransposition II Transposon a Structure b Characteristics c Inverted repeats III Gene conversion a Methods of gene conversion b Location IV Homologous recombination a Recombinant chromosome b Heteroduplex region c Holliday model vs double strand break model d Holliday junction e Sister chromatid exchange Current Lecture I Modes of transposition These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute II III IV a Simple transposition also known as cut and paste transposition using the enzyme transposase to cut out the transposon and prepare the target site on the chromosome b Retrotransposition the process of transcribing the transposon into an RNA intermediate then converting it back to DNA using the enzyme reverse transcriptase Transposon a Structure flanked by direct repeats inverted repeats are not part of the transposon b Characteristics also called jumping genes Require a special enzyme to be transposed c Inverted repeats necessary for transposition in simple transposons because they are recognized by the enzyme transposase which is responsible for transposing the transposon Gene conversion when one allele is converted to the allele on the homologous chromosome a Methods of gene conversion can occur via the mechanism of gap repair synthesis or DNA mismatch repair b Location in the double strand break model the gene conversion is more likely to occur near the break Homologous recombination a Recombinant chromosome derived from a crossover between homologous chromosomes and contain a combination of alleles that is different from the parental chromosomes b Heteroduplex region created by the migration of the Holliday junction Length is determined by the extent to which the junction moves This region does not always contain base pair mismatches because the two homologous chromosomes can be identical in the region of heteroduplex c Holliday model vs double strand break model the key difference between the two models is how the DNA is initially broken In the Holliday model the DNA gets nicked in to analogous locations where in the double strand break model the DNA is uniformly cut across the two strands d Holliday junction an interaction of two strands of DNA from homologous chromosomes e Sister chromatid exchange recombination that occurs between two identical sister chromatids For this reason it does not result in new combinations of alleles since the alleles of the parental chromosomes are identical
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