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74 Cards in this Set
- Front
- Back
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what is a mutation |
heritable change in DNA sequence that can lead to a change in phenotype |
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what is phenotype |
the observable properties of an organism |
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what is a mutant |
a strain of any cell or virus differing from parental strain in genotype (nucleotide sequence of genome) |
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what is wild type strain |
typically refers to strain isolated from nature |
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why is perfect fidelity in organisms counterproductive |
it prevents evolution |
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what does auxotroph mean |
unable to grow on a medium lacking certain nutrients, have to supplement antibiotic in the medium |
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what are selectable mutations |
those that give the mutant a growth advantage under certain conditions |
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what are non selectable mutations |
those that usually have neither an advantage nor a disadvantage over the parent |
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how to detect non selectable mutations |
examining a large number of colonies and looking for differences (screening) |
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what are induced mutations |
those made environmentally or deliberately
can result from exposure to natural radiation or oxygen radicate |
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what are spontaneous mutations |
those that occur without external intervention |
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what are point mutations |
mutations that change only 1 base pair
can lead to single amino acid change in a protein, an incomplete protein |
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why is screening always more tedious than selection |
methods are available to facilitate screening
replica plating is useful for identifying cells with a nutritional requirement for growth (auxotroph) |
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what is a silent mutation |
does not affect amino acid sequence |
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what is a missense mutation |
amino acid changed; polypeptide is incomplete |
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what is a frameshift mutation |
deletions or insertions that result in a shift in the reading frame
often result in complete loss of gene function |
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point mutations are typically what |
reversible |
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what is reversion |
alteration in dna that reverses the effects of a prior mutation |
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what is revertant |
strain in which the original phenotype is restored |
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what is revertant |
strain in which the original phenotype is restored |
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what is same site revertant |
mutation is at same site as original mutation |
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what is revertant |
strain in which the original phenotype is restored |
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what is same site revertant |
mutation is at same site as original mutation |
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what is second site revertant |
mutation is at a different site in the dna |
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what is suppressor |
mutation that compensates for the effect of the original mutation |
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what is suppressor |
mutation that compensates for the effect of the original mutation |
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why do rna viruses have high error rates |
they have their genetic info as rna, almost no rna polymerase has proofreading, the exception is coronavirus |
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what does the ames test do |
makes practical use of bacterial mutations to detect for potentially hazardous chemicals |
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what does the ames test look for |
an increase in mutation of bacteria in the presence of suspected mutagen
a whole variety of chemicals have been screened for toxicity and carcinogenicity |
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what are mutagens |
chemical, physical or biological agents that increase mutation rates |
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what are mutagens |
chemical, physical or biological agents that increase mutation rates |
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nucleotide base analogs |
resemble nucleotides |
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what are mutagens |
chemical, physical or biological agents that increase mutation rates |
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nucleotide base analogs |
resemble nucleotides |
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chemical mutagens : |
- that induce chemical modifications (eg nitrosoguanidine)
- that cause frameshift mutations (intercalating agents such as acridines) |
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nonionizing mutagenic electromagnetic radiation |
- uv radiation - purines and pyrimidines strongly absorb uv -pyrimidine dimer is 1 effect of uv radiation |
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ionizing mutagenic electromagnetic radiation |
- x-rays, cosmic rays, gamma rays - ionize water and produce free radicals -free radicals damage micromolecules in the cell |
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direct reversal |
mutated base is still recognisable and can be repaired without referring to other strand |
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direct reversal |
mutated base is still recognisable and can be repaired without referring to other strand |
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repair of single strand damage |
damaged dna is removed and repaired using opposite strand as template |
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repair of single strand damage |
damaged dna is removed and repaired using opposite strand as template |
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repair of double strand damage |
a break in the dna requires more error-prone repair mechanisms |
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what mechanism is used when dna damage is large enough to interfere with dna replication |
the SOS regulatory system which is more error prone |
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repair of single strand damage |
damaged dna is removed and repaired using opposite strand as template |
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SOS regulatory system |
- allows replication to proceed and cell to replicate but errors are more likely - translesion synthesis allows dna to be synthesised with no template |
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recombination |
physical exchange of dna between genetic elements |
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homologous recombination |
- process that results in genetic exchange between homologous dna from 2 different sources - selective medium can be used to detect rare genetic recombinants |
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mobile dna transposable elements |
discrete segments of dna that move as a unit from one location to another within other dna molecules |
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mobile dna transposable elements |
discrete segments of dna that move as a unit from one location to another within other dna molecules |
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where can transposable elements be found |
in all 3 domains of life |
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how are transposable elements moved |
by transposition |
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mobile dna transposable elements |
discrete segments of dna that move as a unit from one location to another within other dna molecules |
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where can transposable elements be found |
in all 3 domains of life |
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how are transposable elements moved |
by transposition |
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transposition frequency |
1 in 1000 to 1 in 10,000,000 |
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what are the 2 main types of transposable elements in bacteria |
transposons and insertion sequences both carry genes encoding transposase both have inverted repeats at their ends |
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how many insertion sequences do transposons have |
2 |
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insertion sequences |
~ 1000 nucleotides long only gene is for the transposase |
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where are insertion sequences found |
in plasmids and chromosomes of bacteria and archaea in some bacteriophages |
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what does transposase do |
move any dna between inverted repeats |
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what does insertion of a transposable element do |
generates a duplicate target sequence may include antibiotic resistance |
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conservative transposon mechanism |
transposon is excised from one location and reinserted at a second location, number of transposons stays constant |
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replicative transposition mechanism |
a new copy of transposon is produced and inserted at a second location, number of transposons present doubles |
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how are transposons used to make mutants |
transposons with antibiotic resistance are used |
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how are transposons used to make mutants |
transposons with antibiotic resistance are used |
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where is the transposon when making a mutant |
on a plasmid that cannot be replicated in the cell (temperature sensitive replicon) |
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how are transposons used to make mutants |
transposons with antibiotic resistance are used |
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where is the transposon when making a mutant |
on a plasmid that cannot be replicated in the cell (temperature sensitive replicon) |
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most insertions will be in what |
genes that encode proteins |
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mutated gene is tagged with what |
resistance number |
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CRISPR |
clustered regulatory interspaced short palindromic repeats |
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what is CRISPR |
type of prokaryotic immune system |
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what does CRISPR do |
protect bacteria from viruses |
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CRISPR associated proteins (cas proteins) |
obtain and store segments of foreign dna as spacers recognise and destroy foreign dna |
