periods of time however if a base existed in the rare form at the moment that

Periods of time however if a base existed in the rare

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Base Substitutions Transition (4 possible) replaces pyrimidine with anther pyrimidine or purine for another purine Transversion (8 possible) replaces pyrimidine with a purine or vice versa Base substitutions can lead to different changes in amino acids: Silent mutation : single base pair mutation that does not lead to change in amino acid Mis-sense mutation : single bas pair mutation that leads to a different amino acid Non-sense mutation : mutation that results in a stop codon, leading to truncated polypeptide Frameshift mutation : base-pair additions and deletions within the coding regions of genes; they alter the reading frame of all base-pair triplets Mutation Frequency Spontaneous mutations are infrequent o bacteria and phage: 10 -8 to 10- per nucleotide pair per generation o eukaryotes: 10 -7 to 10 -9 per nucleotide pair per generation, or 10 -4 to 10 -6 per gene per generation (an average gene of 1000 bp) Treatment of bacteria with mutagens can increase the mutation frequency to > 1% per gene Factors influencing the rate of spontaneous mutations Accuracy of the DNA replication machinery Efficiency of the mechanisms for the repair of damaged DNA Degree of exposure to mutagenic agents in the environment Mutation and Repair (Chapter 13) Muller Demonatration : X-rays induced mutations in Drosophila Three components of CIB chromsomes o C, for cross-over suppressor o I recessive lethal mutation o B bar-eye phenotype (dominant) Male with CIB dies If lethal only female progeny Non lethal female to mal ratio of 2:1 (sine males with CIB die) Mutations induced by radiation Proportion of electromagnetic spectrum with wavelengths shorter and of higher energy than visible light is subdivide into ionizing radiation (X-rays, gamma, cosmic rays) and nonionizing radiation (UV light) X0rays uncude mutations though ionization UV light induces mutations through excitation
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shorter wavelengths - higher energy Irradiation dosage and mutation frequency Ionization radiation breaks chromosomes and can cause deletions duplications inversions, and translocations These types of mutations display single-hit kinetics o Each mutation results from a single ionization event, that is every ionization has a fixed probability of inducing a mutation
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