GEN 3022 1st Edition Lecture 29Outline of Last Lecture I. Nature of mutationsa. Characteristics of mutationsb. Gene expressionII. Types of mutationsa. Missense mutationsb. Germ-line mutationc. Conditional mutationd. Position effecte. Silent mutationf. Neutral mutationg. Frameshift mutationh. Nonsense mutationIII. Mutation ratea. Ames testIV. DNA repaira. DNA polymerase b. Non-homologous end joiningc. Removal of segment of DNAd. Base excision repaire. DNA mismatch repairOutline of Current LectureI. Genetic recombinationII. Homologous recombinationa. Mechanismb. Sister chromatid exchangec. Holliday modeld. Newer studiesIII. Site-specific recombinationIV. Gene conversiona. MechanismV. Transposition a. Transposable elementsThese 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.i. DNA sequencesii. Mutation and evolutioniii. Debate of evolutioniv. Proliferation of transposable elementsb. McClintock studiesc. Transposition pathwaysi. Simple transpositionii. Retrotranspositiond. TransposaseCurrent LectureI. Genetic recombination: involves chromosomes breaking and rejoining to form new combinations. Three main types are homologous recombination, site-specific recombination, and transposition.II. Homologous recombination: crossing over occurs in meiosis I and occasionally duringmitosis. Found in all species, but the cells of any given species may have more than one molecular mechanism for homologous recombination.a. Mechanism: a pair of homologous chromosomes align, followed by a breakage atanalogous locations and exchange of corresponding segments. b. Sister chromatid exchange: crossing over between sister chromatids. These chromatids are genetically identical to each other, so this exchange does not produce a new combination of alleles. c. Holliday model: involves alignment of homologous chromosomes, nicking at identical locations, strand, invasion, and finally branch migration. d. Newer studies: modified initiation phase of recombination in which one DNA helix is nicked or both strands are broken.III. Site-specific recombination: occurs when small segments of DNA called transposons move to multiple positions within the host’s chromosomal DNA. IV. Gene conversion: when one of the alleles is converted to the other allele, caused by genetic recombination. a. Mechanisms: DNA mismatch repair and DNA gap repair synthesisV. Transposition: involves the integration of small segments of DNA into the chromosome. Can occur at many different locations within the genome. a. Transposable elements: small, mobile segments of DNA involved in transposition.Also known as “jumping genes”.i. DNA sequences: organized in several different ways. Inverted repeats are identical to the original sequence but run in the opposite direction. Directrepeats are exact copies of the original sequence. Insertion element is thesimplest type of transposable element. Long terminal repeats are very long sequences (few hundred nucleotides in length). ii. Mutation and evolution: over the past few decades, researchers have found that transposable elements probably occur in the genomes of all species. iii. Debate of evolution: either transposable elements exist just because theycan (like parasites) or they exist because they offer an advantage to the organism (like antibiotic-resistance). The first theory is called the selfish DNA theory.iv. Proliferation of transposable elements: in mammals, long interspersed elements are usually 1,000 to 10,000 bp long and found in a few thousand to several hundred thousand copies, making up almost 17% of the human genome. Short interspersed elements are less than 500 bp in length and are present in about 1 million copies in the human genome.b. McClintock studies: identified transposable elements in her studies of corn in the1950sc. Transposition pathways: many transposable elements have been found in bacteria, fungi, plant, and animal cells. i. Simple transposition: called “cut and paste” because the transposon is excised and moved to another location. This mechanism is found widely in bacteria and eukaryotes and can increase copy number if the transposition occurs after the replication fork has passed through the transposition element, resulting in two copies of the transposition element in one genome. ii. Retrotransposition: transposable elements move via an RNA intermediate(reverse transcriptase and integrase). The types of elements moved are called retroelements, retrotransposons, or retroposons. Very common, but only in eukaryotes.d. Transposase: enzyme that catalyzes the removal of a transposable element and its reinsertion at another location by recognizing the inverted repeats at the endsof a transposable element and bringing them close