Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages

Sanders - Genetic Analysis: An Integrated Approach 3rd Edition

Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172당신이 사용하는 게 아니라요?교과서 변경

Sanders 3rd Edition

Ch. 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages

문제 24b

6장, 문제 24b

The phage P1 is used as a generalized transducing phage in an experiment combining a donor strain of E. coli of genotype leu⁺ phe⁺ ala⁺ and a recipient strain that is leu⁻ phe⁻ ala⁻. In separate experiments, transductants are selected for leu⁺ (Experiment A), for ala⁺ (Experiment B), and for phe⁺ (Experiment C). Following selection, transductant genotypes for the unselected markers are identified. The selection experiment results below show the frequency of each genotype.

Determine the order of genes on the donor chromosome.

검증된 단계별 안내

Step 1: Understand the problem. The goal is to determine the order of genes (leu, phe, ala) on the donor chromosome based on the frequencies of co-transduction observed in the experiments. Co-transduction frequency is inversely proportional to the physical distance between genes on the chromosome.

Step 2: Analyze Experiment A (selection for leu⁺). The frequencies of phe⁺ and ala⁺ in the transductants indicate how closely these genes are linked to leu. Higher frequencies suggest closer linkage. For example, phe⁺ appears in 50% of transductants, while ala⁺ appears in only 19%, suggesting phe is closer to leu than ala.

Step 3: Analyze Experiment B (selection for ala⁺). The frequencies of leu⁺ and phe⁺ in the transductants indicate how closely these genes are linked to ala. Leu⁺ appears in 48% of transductants, while phe⁺ appears in 0%, suggesting leu is closer to ala than phe.

Step 4: Analyze Experiment C (selection for phe⁺). The frequencies of leu⁺ and ala⁺ in the transductants indicate how closely these genes are linked to phe. Leu⁺ appears in 21% of transductants, while ala⁺ appears in 0%, suggesting leu is closer to phe than ala.

Step 5: Combine the results from all experiments to deduce the gene order. Based on the co-transduction frequencies, the gene order on the donor chromosome is likely leu - phe - ala, with leu being closest to phe and ala being the farthest.

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주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Transduction

Transduction is a process of genetic transfer in bacteria where bacteriophages (viruses that infect bacteria) mediate the transfer of DNA from one bacterium to another. In generalized transduction, any bacterial gene can be transferred, allowing for the mapping of genes based on the frequency of co-transduction. Understanding this process is crucial for analyzing the results of the experiments involving the E. coli strains.

Gene Mapping

Gene mapping is the process of determining the relative positions of genes on a chromosome. In this context, the frequency of co-transduction events can be used to infer the order of genes based on how often they are transferred together. The closer two genes are on a chromosome, the higher the likelihood they will be co-transduced, which is essential for deducing their arrangement.

Genotype Frequencies

Genotype frequencies refer to the proportion of different genotypes in a population or sample. In the experiments described, the frequencies of various genotypes among the transductants provide insights into the genetic linkage and order of the genes. Analyzing these frequencies helps in determining which genes are more likely to be inherited together, thus revealing their relative positions on the chromosome.

관련 실천

교과서 질문

Define the term genetic complementation.

Does the term genetic complementation have the same meaning in both cases? Explain.

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교과서 질문

The phage P1 is used as a generalized transducing phage in an experiment combining a donor strain of E. coli of genotype leu⁺ phe⁺ ala⁺ and a recipient strain that is leu⁻ phe⁻ ala⁻. In separate experiments, transductants are selected for leu⁺ (Experiment A), for ala⁺ (Experiment B), and for phe⁺ (Experiment C). Following selection, transductant genotypes for the unselected markers are identified. The selection experiment results below show the frequency of each genotype.

In Experiment B, why are there no transductants with the genotype leu⁻ ala⁺?

844

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교과서 질문

Synthesis of the amino acid histidine is a multistep anabolic pathway that uses the products of 13 genes (hisA to hisM) in E. coli. Two independently isolated his^- E. coli mutants, designated his1⁻ and his2⁻ are studied in a conjugation experiment. A his⁺ F' donor strain that carries a copy of the hisJ gene on the plasmid is mated with a his1⁻ recipient strain in Experiment 1 and with a his2⁻ recipient in Experiment 2. The exconjugants are grown on plates lacking histidine. Growth is observed among the exconjugants of Experiment 2 but not among those of Experiment 1.

Why is growth observed in Experiment 2 but not in Experiment 1?

586

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교과서 질문

The phage P1 is used as a generalized transducing phage in an experiment combining a donor strain of E. coli of genotype leu⁺ phe⁺ ala⁺ and a recipient strain that is leu⁻ phe⁻ ala⁻. In separate experiments, transductants are selected for leu⁺ (Experiment A), for ala⁺ (Experiment B), and for phe⁺ (Experiment C). Following selection, transductant genotypes for the unselected markers are identified. The selection experiment results below show the frequency of each genotype.

What compound or compounds are added to the minimal medium to select for transductants in Experiments A, B, and C?

705

views

교과서 질문

The phage P1 is used as a generalized transducing phage in an experiment combining a donor strain of E. coli of genotype leu⁺ phe⁺ ala⁺ and a recipient strain that is leu⁻ phe⁻ ala⁻. In separate experiments, transductants are selected for leu⁺ (Experiment A), for ala⁺ (Experiment B), and for phe⁺ (Experiment C). Following selection, transductant genotypes for the unselected markers are identified. The selection experiment results below show the frequency of each genotype.

Diagram the crossover events that form each of the transductants in Experiment A.

716

views

교과서 질문

Synthesis of the amino acid histidine is a multistep anabolic pathway that uses the products of 13 genes (hisA to hisM) in E. coli. Two independently isolated his^- E. coli mutants, designated his1⁻ and his2⁻ are studied in a conjugation experiment. A his⁺ F' donor strain that carries a copy of the hisJ gene on the plasmid is mated with a his1⁻ recipient strain in Experiment 1 and with a his2⁻ recipient in Experiment 2. The exconjugants are grown on plates lacking histidine. Growth is observed among the exconjugants of Experiment 2 but not among those of Experiment 1.

What is the genotype of exconjugants in Experiment 2?

426

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