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Cards In This Set
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General strategy to map genes
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Cross strains containing different genetic markers
-detect recombinants to determine the recombination frequency -determine the map distance |
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Why does genetic exchange occur by a parasexual process in Bacteria?
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bacteria dont undergo meiosis since they are haploid
cant exchage DNA during prophase like eukaryotes |
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How are linear molecules incorporated into the bacteria chromosome?
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Double crossover: replaces bacterial verison of DNA fragement
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How are cicurlar plasmids incorporated into bacterial chromosomes?
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Single cross over
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Three mechanisms that bacteria use to exchange genes and what all of these processes have in common
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1. transformation
2. conjugation 3. transduction -transfer is always unidirectional -a partial diploid is formed -only the genes on the bacterial chromosome are inherited, other exchange product is degraded |
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Two types of transformation
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1. natural: bacterium has machinery to take up DNA
2. engineered: bacterium can be manipulated to take up foreign DNA |
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Three species that natural transformation has been observed in
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Bacillus subtilis
Streptoccocus pneumoniae Haemophilus influenza Neiseria gonorrhoeae |
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Mechanism of transformation
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1. Requires energy
2.MUST have receptors and enzymatic mahinery to bind free DNA molecuels and transport into cytoplasm 3. Only competent cells can take up DNA 4. competence factor (transcription factor that activates the 8-10 genes needed to make the receptor complex) is secreated during early-log phase 5. recepor proteins are transported to the cell surface. Receptors recognized the external DNA and bind to it 5. foreign DNA is translocated into the bacterium |
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Mechanism for recognizing and taking up foreing DNA in GRAM NEG bacteria. Haemophilus influenza and Neiseria gonorrhoeae
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11 bp and 10 bp sequence are recognized
double strand DNA is incorporated into the cell. one strand is degraded |
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Mechanism for recognizing and taking up foreign DNA in GRAM POS bacteria. Bacillus subtilis and Streptoccous pneumonia
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Take up and foreing DNA >750 bp
only 1 strand is introcuded into the recipient. the other strand is degraded by a cellular exonuclease before it enters the cell |
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Transformation and mapping genes and its limitations
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Method: measure the cotransformation frequency as the donor DNA concentration is decreased
-rate of linked genes will decrease linearly -rate of double transformation will decrease exponentially limitations: -only works for tightly linked genes that enter the cell together on the same DNA fragement -dificult and tedious |
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Requirements for conjugation
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1. cell to cell contact
2.recombination via double cross over |
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Lederberg and Tatum's experiment, the possible mechanisms of obtaining prototrophs, and their conclusions
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experiment: mixed two auxotrops together in complete media and selevted for prototrops on minimal media
mechanism for obtaining prototrophs: -would require 2 separate strains/ events -frequency would need to be double conclusions: -ruled out reversion b/c frequency was not double -ruled out transforamation b/c isolated naked DNA from each strand and they never transformed -had to be unknown mechanism |
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What did Bernard Davis discover about conjugation?
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Concluded that bacteria must have physical contact ( U tube experiment)
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What did William Hayes discover that is required for conjugation and what is known about his element?
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identified the fertility factor (F): it is a 94.5 kb plasmid that contains all the genes required to form sex pilus
-contains two origins of replication -ori V: makes additional copes of F during vegetative growth -ori T: transfers F DNA into F- recipient through sex pilus |
