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31 Cards in this Set

  • Front
  • Back
Describe a mutation.
*heritable change in DNA sequence that can lead to a change in phenotype
How does a mutation differ from its parent strain?
*carries a change

*in genotype(the nucleotide sequence of the genome)
What is a wild type strain?
a strain isolated from a natural environment without genetic manipulations
What are selectable mutations?
*those that give the mutant a growth advantage under certain environmental conditions

*are especially useful in genetic research
What is "screening" used for?
*when selection is not possible, mutants must be identified by screening

*examination of large number of colonies to detect the mutant strains
Describe a spontaneous mutation.
result from exposure to natural radiation, free radicals etc
What is a point mutation?
*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
What is a silent mutation
*usually occurs in the third base of a codon and do not affect the primary sequence of the protein
What is the difference between a nonsense and a missense mutation?
*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
What are the 3 most common mutations (in order)?
Missense mutations are more common then followed by nonsense and then silent mutations
What are the typical rates for mutations?
For a typical bacterium, mutation rates of 10–7 to 10–11 per base pair are generally seen
Explain a frameshift mutation.
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
Describe mutagens.
*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
What are examples of mutagens?
*UV radiation and Xray forms dimmers in Pyrimidines

*Acridine and ethidium bromide inserts between bases
What are the 3 mechanisms of recombination?
*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
What is recombination?
exchange of genes between genetic elements
How does homologous recombination arise?
when closely related DNA sequences from two distinct genetic elements are combined in a single element
Describe transduction and its 2 types.
*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
Describe plasmids.
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
What is conjugation?
mechanism of DNA transfer in prokaryotes that requires cell-to-cell contact
Describe how plasmids work with conjugation?
Describe transposons?
genetic elements that can move from one location on a chromosome to another by a process called transposition, a type of site-specific recombination
Explain the 2 types of transposition?

How are transposons important?
carry genes encoding antibiotic resistance, and they can be used as biological mutagens
How is a plasmid or virus used as the cloning vector?
Describe in vitro recombination?
uses restriction enzymes and DNA ligase to produce the hybrid DNA molecule
What is shotgun cloning?
Making a gene library by cloning random fragments of a genome
How are plasmids used as cloning vectors?
How is bacteriophage Lambda used as a cloning vector?
Describe site-directed mutagenesis.
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
What can cause gene disruption?
Inserting DNA fragments, called cassettes, into genes