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Question 1 of 10
Animation Assessment
Question
If 1 million F- bacteria received an F factor through conjugation with F+ bacteria, how many of these would be expected to become Hfr bacteria?
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Correct. About 1 in 10,000 recipients of the F factor will integrate the F factor episome and become Hfr bacteria. Therefore, if there were 1 million recipients we would expect approximately 100 Hfr bacteria to result.
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Incorrect. About 1 in 10,000 recipients of the F factor will integrate the F factor episome and become Hfr bacteria. Therefore, if there were 1 million recipients we would expect approximately 100 Hfr bacteria to result.
Question
What best describes the most common fate of an F- bacterium after conjugation with an Hfr bacterium?
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Correct. In most cases the F- recipient, resulting from a conjugation with an Hfr donor, will remain F- because the entire F-factor is only rarely transferred. However, the bacterial chromosomal genes coming into the recipient provides the opportunity for recombination that may change the phenotype of the recipient F- bacterium.
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Incorrect. In most cases the F- recipient, resulting from a conjugation with an Hfr donor, will remain F- because the entire F-factor is only rarely transferred. However, the bacterial chromosomal genes coming into the recipient provides the opportunity for recombination that may change the phenotype of the recipient F- bacterium.
Question
If lac+ Hfr bacteria mated with a lac- F- bacteria in an interrupted mating experiment, the F- bacteria will only gain the ability to metabolize lactose if a copy of the lac+ gene recombines with the F- bacteria’s chromosome. Why is recombination into the bacterial chromosome necessary?
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Correct. The lac+ gene from the Hfr bacteria will enter the F- bacteria as a linear piece of DNA which is unstable in bacteria. The lactose-metabolizing genes are perfectly active on a circular plasmid or on the bacterial chromosome. In most cases the F- bacteria will remain F- after an interrupted mating experiment.
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Incorrect. The lac+ gene from the Hfr bacteria will enter the F- bacteria as a linear piece of DNA which is unstable in bacteria. The lactose-metabolizing genes are perfectly active on a circular plasmid or on the bacterial chromosome. In most cases the F- bacteria will remain F- after an interrupted mating experiment.
Question
Which of the following statements is FALSE about the conjugation of an Hfr bacterium and an F- bacterium?
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Correct. Following the nick in the Hfr bacterium’s chromosome, the free 5’ end (leading strand) of the donor moves through the transfer pore into the F- recipient bacterium. As a result, those genes that follow the free 5’ end of the nicked DNA strand are more likely to be transferred than those near the 3’ end of the nick which would only enter the F- bacterium if the entire chromosome is transferred, which happens only rarely.
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Incorrect. Following the nick in the Hfr bacterium’s chromosome, the free 5’ end (leading strand) of the donor moves through the transfer pore into the F- recipient bacterium. As a result, those genes that follow the free 5’ end of the nicked DNA strand are more likely to be transferred than those near the 3’ end of the nick which would only enter the F- bacterium if the entire chromosome is transferred, which happens only rarely.
Question
Which of the following features are essential to map the bacterial chromosome in a single interrupted mating experiment?
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Correct. When performing a single interrupted mating experiment, all of the Hfr bacteria must be from the same strain, and all of the mating must occur at approximately the same time in order to ensure that the same donor genes are moving into the recipient bacteria at approximately the same rate. The remaining Hfr bacteria must be eliminated through selection. The order of traits transferred to the F- bacterium can be deduced by comparing the phenotypes of different batches of bacteria where mating was interrupted at different time points.
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Incorrect. When performing a single interrupted mating experiment, all of the Hfr bacteria must be from the same strain, and all of the mating must occur at approximately the same time in order to ensure that the same donor genes are moving into the recipient bacteria at approximately the same rate. The remaining Hfr bacteria must be eliminated through selection. The order of traits transferred to the F- bacterium can be deduced by comparing the phenotypes of different batches of bacteria where mating was interrupted at different time points.
Question
Which of the following can be accomplished by an interrupted mating experiment between Hfr and F- bacteria?
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Correct. Interrupted mating experiments can only provide information about the donor, Hfr chromosome. Interrupted mating experiments provide no information about DNA sequence or genome size but can determine the gene order on the Hfr chromosome.
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Incorrect. Interrupted mating experiments can only provide information about the donor, Hfr chromosome. Interrupted mating experiments provide no information about DNA sequence or genome size but can determine the gene order on the Hfr chromosome.
Question
In the interrupted mating experiment shown in the animation, the strs allele from the Hfr strain enters the F- bacteria before the azir, lac+, and gal+ alleles. Why can you use streptomycin to select for F- recombinant bacteria if the first gene entering the F- bacteria can potentially convert the streptomycin resistant F- strain into a streptomycin sensitive bacterium?
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Correct. Although the strs allele from the donor could recombine with the bacterial chromosome and convert it to streptomycin-sensitive, these recombinants will be eliminated during selection. For linear DNA, as the donor DNA in an Hfr conjugation is, there must be two crossover points for recombination with the bacterial chromosome. If streptomycin is used as a selection agent, the surviving recombinant bacteria must have had both crossover points after the str gene on the donor DNA.
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Incorrect. Although the strs allele from the donor could recombine with the bacterial chromosome and convert it to streptomycin-sensitive, these recombinants will be eliminated during selection. For linear DNA, as the donor DNA in an Hfr conjugation is, there must be two crossover points for recombination with the bacterial chromosome. If streptomycin is used as a selection agent, the surviving recombinant bacteria must have had both crossover points after the str gene on the donor DNA.
Question
An Hfr bacterial strain with a genotype of amps, gal+, leu+, cys+, thr+ was used in an interrupted mating experiment with an F- bacterial strain with genotype ampr, gal-, leu-, cys-, thr-. At regular intervals, the mating was interrupted and bacteria were selected with ampicillin and tested for the transfer of Hfr alleles into the F- bacteria. The time required to transfer the donor genes is shown in the table below.
Gene transferred
Time
cys
3 min
thr
6 min
gal
10 min
leu
12 min
Which of the following can you conclude from this experiment?
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Correct. Since there are four minutes between thr and gal and two minutes between galand leu, the distance between thr and gal is greater than the distance between gal and leu. Although most bacterial chromosomes are circular, this information can’t be obtained from the data given. The order of the genes on the Hfr bacterial chromosome is cys thr gal leu.
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Incorrect. Since there are four minutes between thr and gal and two minutes between galand leu, the distance between thr and gal is greater than the distance between gal and leu. Although most bacterial chromosomes are circular, this information can’t be obtained from the data given. The order of the genes on the Hfr bacterial chromosome is cys thr gal leu.
Question
An Hfr bacterial strain with a genotype of amps, gal+, leu+, cys+, thr+ was used in an interrupted mating experiment with an F- bacterial strain with genotype ampr, gal-, leu-, cys-, thr-. At regular intervals, the mating was interrupted and bacteria were selected with ampicillin and tested for the transfer of Hfr alleles into the F- bacteria. The time required to transfer the donor genes is shown in the table below.
Gene transferred
Time
cys
3 min
thr
6 min
gal
10 min
leu
12 min
What is the order of genes on the Hfr donor chromosome?
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Correct. From the data given, the order of genes on the Hfr donor chromosome is cys thr gal leu, but leu gal thr cys is equally correct. Since most bacterial chromosomes are circular, one can deduce the order of genes, but the orientation of the genes depends on the orientation of the F factor integration site.
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Incorrect. From the data given, the order of genes on the Hfr donor chromosome is cys thr gal leu, but leu gal thr cys is equally correct. Since most bacterial chromosomes are circular, one can deduce the order of genes, but the orientation of the genes depends on the orientation of the F factor integration site.
Question
An Hfr bacterial strain with a genotype of amps, gal+, leu+, cys+, thr+ was used in an interrupted mating experiment with an F- bacterial strain with genotype ampr, gal-, leu-, cys-, thr-. At regular intervals, the mating was interrupted and bacteria were selected with ampicillin and tested for the transfer of Hfr alleles into the F- bacteria. The time required to transfer the donor genes is shown in the table below.
Gene transferred
Time
cys
3 min
thr
6 min
gal
10 min
leu
12 min
Which gene is closest to the leading side of the F factor origin of transfer?
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Correct. Since the cys+ allele from the Hfr strain appears first, this gene is the closest to the F factor origin of transfer.
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Incorrect. Since the cys+ allele from the Hfr strain appears first, this gene is the closest to the F factor origin of transfer.