Podcast
Questions and Answers
What was constructed from the data provided by Wollman and Jacob?
What was constructed from the data provided by Wollman and Jacob?
- A physical map of the chromosome
- A gene expression analysis tool
- A DNA sequencing technology
- A genetic map of the E. coli chromosome (correct)
What is a characteristic of the Hfr strains identified by Wollman and Jacob?
What is a characteristic of the Hfr strains identified by Wollman and Jacob?
- The origin of transfer had been integrated at different places in the chromosome (correct)
- They have a deleted origin of transfer
- They are unable to transfer genes
- They have a mutated origin of transfer
What was the purpose of comparing the order of genes among the Hfr strains?
What was the purpose of comparing the order of genes among the Hfr strains?
- To determine the function of each gene
- To demonstrate the circular nature of the E. coli chromosome
- To identify the origin of transfer
- To verify the genetic map constructed by Wollman and Jacob (correct)
What can be inferred about the genetic map constructed by Wollman and Jacob?
What can be inferred about the genetic map constructed by Wollman and Jacob?
What is the significance of the E. coli strains studied by Wollman and Jacob?
What is the significance of the E. coli strains studied by Wollman and Jacob?
What is the relationship between the origin of transfer and the genetic map constructed by Wollman and Jacob?
What is the relationship between the origin of transfer and the genetic map constructed by Wollman and Jacob?
What is the advantage of using Hfr strains to study gene transfer?
What is the advantage of using Hfr strains to study gene transfer?
Where are the general methods for growing bacteria in a laboratory described?
Where are the general methods for growing bacteria in a laboratory described?
What is the purpose of the appendix in the context of laboratory methods?
What is the purpose of the appendix in the context of laboratory methods?
What is the relationship between the appendix and the main text?
What is the relationship between the appendix and the main text?
Why is the appendix placed at the end of the document?
Why is the appendix placed at the end of the document?
What is the advantage of using an appendix to provide supplementary information?
What is the advantage of using an appendix to provide supplementary information?
What is the primary purpose of including laboratory methods in a document?
What is the primary purpose of including laboratory methods in a document?
When does the lac+ gene enter?
When does the lac+ gene enter?
What is the timing of the gal gene's entry?
What is the timing of the gal gene's entry?
Which gene is transferred first?
Which gene is transferred first?
When does the ton gene enter?
When does the ton gene enter?
What is the order of gene transfer?
What is the order of gene transfer?
How long after the azi s gene enters does the lac+ gene enter?
How long after the azi s gene enters does the lac+ gene enter?
How long after the lac+ gene enters does the gal gene enter?
How long after the lac+ gene enters does the gal gene enter?
What is the correct sequence of gene entry?
What is the correct sequence of gene entry?
How long does it take for all genes to enter?
How long does it take for all genes to enter?
What is the relationship between the timing of gene entry and the genetic map?
What is the relationship between the timing of gene entry and the genetic map?
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Study Notes
Interrupted Conjugation Experiment
- The distance between genes is determined by comparing their times of entry during an interrupted conjugation experiment.
- The approximate time of entry is computed by extrapolating the time back to the x-axis.
- In this example, the two genes are approximately 9 minutes apart along the E. coli chromosome.
Genetic Map Construction
- A genetic map was constructed from the data obtained from the interrupted conjugation experiment.
- Wollman and Jacob constructed the genetic map based on the experiment's results.
Hfr Strains
- Hfr (High Frequency of Recombination) strains were identified, which had the origin of transfer integrated at different places in the E. coli chromosome.
- Comparison of the order of genes among these Hfr strains demonstrated the genetic mapping of the E. coli chromosome.
Genetic Transfer and Mapping in Bacteria
- Luca Cavalli-Sforza discovered a strain of E. coli in the 1950s, which led to the development of conjugation and mapping via Hfr strains.
Conjugation and Mapping via Hfr Strains
- Hfr (High Frequency of Recombination) strains are used in conjugation experiments to map genes in bacteria.
- The process involves the transfer of genes from an Hfr cell to an F- (recipient) cell.
- The time it takes for genes to first enter an F- recipient during conjugation is measured in minutes.
- A simplified genetic map of E. coli can be constructed using conjugation experiments.
Figures
- Figure 7.6 illustrates the transfer of bacterial genes from an Hfr cell to an F- cell.
- Figure 7.8 shows a simplified genetic map of E. coli.
Interrupted Conjugation Experiment
- The distance between genes is determined by comparing their times of entry during an interrupted conjugation experiment
- Approximate time of entry is computed by extrapolating the time back to the x-axis
- In this example, two genes are approximately 9 minutes apart along the E. coli chromosome
Conjugation between Hfr and F- Strains
- Conjugation between an Hfr and an F- strain involves the transfer of a portion of the Hfr bacterial chromosome
- The origin of transfer of the integrated F factor determines the starting point and direction of the transfer process
- When the DNA is cut, or nicked, at this site, it becomes the starting point for the transfer of the Hfr chromosome to the F- cell
- A strand of bacterial DNA begins to enter the recipient cell in a linear manner
Transfer of Chromosomal Material
- It generally takes about 1.5 to 2 hours for the entire Hfr chromosome to be passed into the F- cell
- Most conjugations do not last that long, only a portion of the Hfr chromosome gets into the F- cell
- Chromosomal material from the Hfr cell can recombine with the homologous region on the chromosome of the recipient cell
Transfer of Bacterial Genes
- Genotype of Hfr cell: lac + (ability to metabolize lactose) and pro + (ability to synthesize proline)
- Genotype of F- cell: lac - (inability to metabolize lactose) and pro - (inability to synthesize proline)
Transfer of Genes from Hfr to F- Cell
- The azi s gene is transferred
- The ton gene is transferred
- The lac + gene enters between 15 and 20 minutes
- The gal gene enters between 20 and 25 minutes
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