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BIOL 239 Quiz: Set 19- Mutations

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BIOL 239
Christine Dupont

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Mutations  What are mutations o Heritable changes in base sequences that modify the information content of DNA used to identify mutations, we first need to identify what the 'normal' or 'wildtype' allele is Heritable from cell to cell not just parent to child  What is a wild type allele? o There is still some disagreement as to how this is defined o Generally, it is the allele(s) that dominates in a wild population o Others consider any allele present in more than 1% of the population to be a wildtype allele o Wildtype alleles can be recessive or dominant o Dominant and recessive are really a reflection of what goes on at the molecular level. A dominant allele usually masks the presence (effect) of the recessive allele. o More than one wildtype allele can exist for a gene = polymorphic gene  e.g., seed coat colour in Indian corn  What are the different kinds of mutations? o a) Substitution: o 1. Transition: Purine for Purine; Pyrimidine for Pyrimidine o 2. Transversion: Purine for Pyrimidine; Pyrimidine for Purine  b) Deletion  c) Insertion  d) Inversion - Upside-down and backwards, may or may not impact the phenotype  e) Reciprocal translocation - Part of one chromosome has been replaced with a region from another chromosome and vice versa -changing places  Error! Filename not specified.  How frequent are mutations? o In general, mutation rates fall into the r-12e of-6 2 x 10 mutations per gene, per generation o Can vary between <10 to >10 depending on the gene and species  How would you estimate rates of mutations of a particular gene? o Inbreed homozygous recessive for a trait --> produce lots of offspring to see change in phenotype o Of course, many mutations occur that do not affect phenotype (most mutations are not in genes) o The only way to detect these is through molecular methods e.g. DNA sequencing  Issue with evolution? o Evolution is the change in the inherited characteristics of populations over generations o But what is the mechanism? Is the selective pressure causing the adaption? Or was it already there and just uncovered?  Describe the Luria-Delbruc ̈k 'Jackpot' or Fluctuation hypotheses o Set up small vials of bacterial culture and let them grow for a specified amount of time, to let whatever mutations there continue then at the end add equal portions of each culture to plates containing media along with phage that kills them o observed the results The virus is the selective pressure o Questions: How/why do the resistant colonies appear o Hypothesis #1: Adaption is a physiological response to phage pressure - Should see low numbers in colonies but found in all Believes that resistance is the result of active adaptation to the selective pressure (phage) o based on Lamarck's theory of evolution by acquired traits o The selective pressure causes/drives the mutation o e.g., if you develop large muscles as a result of delivering refrigerators for a living, then your offspring will also have large muscles o If so, then all plated cultures should adapt similarly, resulting in similar numbers of resistant colonies Black colonies have a resistant mutation for phage resistance o Hypothesis #2 Resistance is a result of random mutations, << Proved right o Exclusive of the selective pressure  Based on Darwin's theory of evolution of natural variation and selection  If so, then there will be differences in the numbers of resistant colonies obtained due to random mutation  Error! Filename not specified.  Conclusions from Luria-Delbruc ̈k 'Jackpot' or Fluctuation test o Resistance occurs as a result of random, spontaneous mutations that happen at various time points before exposure to the selective agent (selective pressure is not causing the mutation) o Found varied number of colonies remaining o Mutations occurring early in the growth of the liquid culture, resulted in many resistant colonies when plated; those occurring late resulted in few resistant colonies (fluctuations in numbers obtained)  Describe verification via replication plating o No penicillin in master plate (nutrient agar) o Copy paste multiple times into different plates of agar o If in different places its active evolution and supports Lemark o If in same place, then proves Darwin because
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