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 19b

6장, 문제 19b

An Hfr strain with the genotype cys⁺ lue⁺ met⁺ str^S is mated with an F^- strain carrying the genotype cys⁻ lue⁻ met⁻ strᴿ. In an interrupted mating experiment, small samples of the conjugating bacteria are withdrawn every 3 minutes for 30 minutes. The withdrawn cells are shaken vigorously to stop conjugation and then placed on three different selection media, composed as follows:

Medium 1: Minimal medium plus leucine, methionine, and streptomycin
Medium 2: Minimal medium plus cysteine, methionine, and streptomycin
Medium 3: Minimal medium plus cysteine, leucine, and streptomycin

List all possible bacterial genotypes growing on each medium.

검증된 단계별 안내

Step 1: Understand the genotypes of the Hfr strain and the recipient strain. The Hfr strain is cys⁺ leu⁺ met⁺ strˢ, meaning it can synthesize cysteine, leucine, and methionine but is sensitive to streptomycin. The recipient strain is cys⁻ leu⁻ met⁻ strᴿ, meaning it cannot synthesize these amino acids but is resistant to streptomycin.

Step 2: Recognize the role of the media. Each medium contains specific supplements and streptomycin. Streptomycin ensures that only the recipient strain (strᴿ) or recombinants (which inherit strᴿ from the recipient) can grow. The supplements in each medium allow growth of bacteria that can synthesize the missing amino acids.

Step 3: Analyze Medium 1 (minimal medium + leucine, methionine, and streptomycin). Bacteria growing here must be able to synthesize cysteine (cys⁺) since leucine and methionine are provided. The possible genotype of bacteria growing on this medium is cys⁺ leu⁻ met⁻ strᴿ.

Step 4: Analyze Medium 2 (minimal medium + cysteine, methionine, and streptomycin). Bacteria growing here must be able to synthesize leucine (leu⁺) since cysteine and methionine are provided. The possible genotype of bacteria growing on this medium is cys⁻ leu⁺ met⁻ strᴿ.

Step 5: Analyze Medium 3 (minimal medium + cysteine, leucine, and streptomycin). Bacteria growing here must be able to synthesize methionine (met⁺) since cysteine and leucine are provided. The possible genotype of bacteria growing on this medium is cys⁻ leu⁻ met⁺ strᴿ.

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이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.

영상 길이:

주요 개념

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

Conjugation in Bacteria

Conjugation is a process of genetic transfer in bacteria where one bacterium transfers genetic material to another through direct contact. This often involves the transfer of plasmids or chromosomal DNA, allowing for the exchange of traits such as antibiotic resistance or metabolic capabilities. Understanding conjugation is crucial for analyzing the genetic outcomes of mating experiments, as it determines which traits can be passed on to the recipient strain.

Hfr Strains

Hfr (high frequency of recombination) strains are bacterial strains that have a plasmid integrated into their chromosomal DNA, allowing them to transfer chromosomal genes to a recipient during conjugation. The order and timing of gene transfer can be mapped based on the time of withdrawal during an interrupted mating experiment. Recognizing the significance of Hfr strains is essential for predicting which genes may be transferred and expressed in the recipient strain.

Selection Media

Selection media are specialized growth environments that allow only certain bacteria to thrive based on their genetic traits. In this experiment, different media are used to select for bacteria that can synthesize specific amino acids or resist antibiotics. By analyzing which genotypes grow on each medium, one can infer the genetic changes that occurred during conjugation and identify the successful gene transfers from the Hfr strain to the recipient strain.

관련 실천

교과서 질문

An Hfr strain with the genotype cys⁺ lue⁺ met⁺ str^S is mated with an F^- strain carrying the genotype cys⁻ lue⁻ met⁻ strᴿ. In an interrupted mating experiment, small samples of the conjugating bacteria are withdrawn every 3 minutes for 30 minutes. The withdrawn cells are shaken vigorously to stop conjugation and then placed on three different selection media, composed as follows:

Medium 1: Minimal medium plus leucine, methionine, and streptomycin

Medium 2: Minimal medium plus cysteine, methionine, and streptomycin

Medium 3: Minimal medium plus cysteine, leucine, and streptomycin

What is the purpose of adding streptomycin to each selection medium?

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교과서 질문

A triple-auxotrophic strain of E. coli having the genotype phe⁻ met⁻ ara⁻ is used as a recipient strain in a transduction experiment. The strain is unable to synthesize its own phenylalanine or methionine, and it carries a mutation that leaves it unable to utilize the sugar arabinose for growth. The recipient is crossed to a prototrophic strain with the genotype phe⁺ met⁺ ara⁺. The table below shows the selected marker and gives cotransduction frequencies for the unselected markers.

Use the cotransduction data to determine the order of these genes.

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교과서 질문

An Hfr strain with the genotype cys⁺ lue⁺ met⁺ str^S is mated with an F^-strain carrying the genotype cys⁻ lue⁻ met⁻ strᴿ. In an interrupted mating experiment, small samples of the conjugating bacteria are withdrawn every 3 minutes for 30 minutes. The withdrawn cells are shaken vigorously to stop conjugation and then placed on three different selection media, composed as follows:

Medium 1: Minimal medium plus leucine, methionine, and streptomycin

Medium 2: Minimal medium plus cysteine, methionine, and streptomycin

Medium 3: Minimal medium plus cysteine, leucine, and streptomycin

What donor gene is the selected marker in each medium?

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교과서 질문

An interrupted mating study is carried out on Hfr strains 1, 2, and 3 identified in Problem 17. After conjugation is established, a small sample of the mixture is collected every minute for 20 minutes to determine the distance between genes on the chromosome. Results for each of the three Hfr strains are shown below. The total duration of conjugation (in minutes) is given for each transferred gene.

Hfr strain 1 oriT met ala lac gal

Duration (min) 0 2 8 13 17

Hfr strain 2 oriT met leu thr azi

Duration (min) 0 2 7 10 17

Hfr strain 3 oriT gal pro trp azi

Duration (min) 0 3 8 14 19

In minutes, what is the total length of the chromosome in the donor species?

1065

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교과서 질문

An Hfr strain with the genotype cys⁺ lue⁺ met⁺ strˢ is mated with an F^- strain carrying the genotype cys⁻ lue⁻ met⁻ strᴿ. In an interrupted mating experiment, small samples of the conjugating bacteria are withdrawn every 3 minutes for 30 minutes. The withdrawn cells are shaken vigorously to stop conjugation and then placed on three different selection media, composed as follows:

Medium 1: Minimal medium plus leucine, methionine, and streptomycin

Medium 2: Minimal medium plus cysteine, methionine, and streptomycin

Medium 3: Minimal medium plus cysteine, leucine, and streptomycin

The following table shows the number of colonies growing on each selection medium. The sampling time indicates how many minutes have passed since conjugation began.

Sampling Time (minutes) Number of Colonies

Plate 1 Plate 2 Plate 3

3 0 0 0

6 0 0 0

9 0 62 0

12 0 87 0

15 51 124 0

18 79 210 62

21 109 250 85

24 144 250 111

27 152 250 122

30 152 250 122

Determine the order of donor genes cys, leu, and met from the interrupted mating data.

697

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교과서 질문

An Hfr strain with the genotype cys⁺ lue⁺ met⁺ strˢ is mated with an F^- strain carrying the genotype cys⁻ lue⁻ met⁻ strᴿ. In an interrupted mating experiment, small samples of the conjugating bacteria are withdrawn every 3 minutes for 30 minutes. The withdrawn cells are shaken vigorously to stop conjugation and then placed on three different selection media, composed as follows:

Medium 1: Minimal medium plus leucine, methionine, and streptomycin

Medium 2: Minimal medium plus cysteine, methionine, and streptomycin

Medium 3: Minimal medium plus cysteine, leucine, and streptomycin

The following table shows the number of colonies growing on each selection medium. The sampling time indicates how many minutes have passed since conjugation began.

Sampling Time (minutes) Number of Colonies

Plate 1 Plate 2 Plate 3

3 0 0 0

6 0 0 0

9 0 62 0

12 0 87 0

15 51 124 0

18 79 210 62

21 109 250 85

24 144 250 111

27 152 250 122

30 152 250 122

Suppose a fourth selection medium containing leucine and streptomycin is prepared. At what sampling time do you expect the first-growing colonies to appear? Explain your reasoning.

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