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31 Cards in this Set
- Front
- Back
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Describe a mutation.
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*heritable change in DNA sequence that can lead to a change in phenotype
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How does a mutation differ from its parent strain?
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*carries a change
*in genotype(the nucleotide sequence of the genome) |
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What is a wild type strain?
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a strain isolated from a natural environment without genetic manipulations
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What are selectable mutations?
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*those that give the mutant a growth advantage under certain environmental conditions
*are especially useful in genetic research |
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What is "screening" used for?
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*when selection is not possible, mutants must be identified by screening
*examination of large number of colonies to detect the mutant strains |
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Describe a spontaneous mutation.
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result from exposure to natural radiation, free radicals etc
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What is a point mutation?
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*a change in a single base pair or base pair substitution
*can lead to a single amino acid change in a polypeptide or to no change at all, depending on the particular codon involved |
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What is a silent mutation
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*usually occurs in the third base of a codon and do not affect the primary sequence of the protein
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What is the difference between a nonsense and a missense mutation?
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*nonsense mutation: the codon becomes a stop codon and an incomplete polypeptide is made
*missense mutation: the sequence of amino acids in the ensuing polypeptide is changed, resulting in an inactive protein or one with reduced activity |
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What are the 3 most common mutations (in order)?
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Missense mutations are more common then followed by nonsense and then silent mutations
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What are the typical rates for mutations?
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For a typical bacterium, mutation rates of 10–7 to 10–11 per base pair are generally seen
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Explain a frameshift mutation.
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a genetic mutation that inserts or deletes a number of nucleotides that is not evenly divisible by three from a DNA sequence. Due to the triplet nature of gene expression by codons, the insertion or deletion can disrupt the reading frame, or the grouping of the codons, resulting in a completely different translation from the original. The earlier in the gene the deletion or insertion occurs, the more altered the gene product is
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Describe mutagens.
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*are chemical, physical, or biological agents that increase the mutation rate
*can alter DNA in many different ways, but such alterations are not mutations unless they can be inherited |
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What are examples of mutagens?
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*UV radiation and Xray forms dimmers in Pyrimidines
*Acridine and ethidium bromide inserts between bases |
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What are the 3 mechanisms of recombination?
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*transformation: free DNA incorporates in a cell introducing genetic changes
*transduction: DNA transfered by a virus *Conjugation: transfer of plasmid DNA by cell to cell contact |
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What is recombination?
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exchange of genes between genetic elements
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How does homologous recombination arise?
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when closely related DNA sequences from two distinct genetic elements are combined in a single element
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Describe transduction and its 2 types.
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*involves the transfer of host genes from one bacterium to another by bacterial viruses
*generalized transduction defective virus particles incorporate fragments of the cell's chromosomal DNA randomly, but the efficiency is low *specialized transduction the DNA of a temperate virus excises incorrectly and takes adjacent host genes along with it. Transducing efficiency in this case may be very high |
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Describe plasmids.
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small circular or linear DNA molecules that carry any of a variety of unessential genes. Although a cell can contain more than one plasmid, they cannot be closely related genetically
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What is conjugation?
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mechanism of DNA transfer in prokaryotes that requires cell-to-cell contact
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Describe how plasmids work with conjugation?
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*
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Describe transposons?
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genetic elements that can move from one location on a chromosome to another by a process called transposition, a type of site-specific recombination
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Explain the 2 types of transposition?
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Replicative:
Conservative: |
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How are transposons important?
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carry genes encoding antibiotic resistance, and they can be used as biological mutagens
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How is a plasmid or virus used as the cloning vector?
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*
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Describe in vitro recombination?
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uses restriction enzymes and DNA ligase to produce the hybrid DNA molecule
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What is shotgun cloning?
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Making a gene library by cloning random fragments of a genome
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How are plasmids used as cloning vectors?
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*
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How is bacteriophage Lambda used as a cloning vector?
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*
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Describe site-directed mutagenesis.
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allows synthetic DNA molecules of desired sequence to be made in vitro and used to construct a mutated gene directly or to change specific base pairs within a gene
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What can cause gene disruption?
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Inserting DNA fragments, called cassettes, into genes
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