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?

Hfr strains that differ in integrated F factor orientation and site of integration are used to construct consolidated bacterial chromosome maps. The data below show the order of gene transfer for five strains.

Hfr Strain   Order of Gene Transfer (First → Last)

Hfr A        oriT–thr–leu–azi–ton–pro–lac–ade

Hfr B        oriT–mtl–xyl–mal–str–his

Hfr C        oriT–ile–met–thi–thr–leu–azi–ton

Hfr D        oriT–his–trp–gal–ade–lac–pro–ton

Hfr E        oriT–thi–met–ile–mtl–xyl–mal–str

Identify the overlaps between Hfr strains. Identify the orientations of integrated F factors relative to one another.

Five Hfr strains from the same bacterial species are analyzed for their ability to transfer genes to F⁻ recipient bacteria. The data shown below list the origin of transfer (oriT) for each strain and give the order of genes, with the first gene on the left and the last gene on the right. Use the data to construct a circular map of the bacterium.

Hfr Strain     Genes Transferred

Hfr 1         oriT met ala lac gal

Hfr 2         oriT met leu thr azi

Hfr 3         oriT gal pro trp azi

Hfr 4         oriT leu met ala lac

Hfr 5         oriT trp azi thr leu met

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

Using the chromosome map you prepared in answer to Problem 17, determine the distance in minutes between each gene on the map.

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

For each Hfr strain, draw a time-of-entry profile.

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

Write out the interrupted mating results you would expect after 20 minutes of conjugation for Hfr strains 4 and 5. Use the format shown at the beginning of this problem.

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

Explain why azi is the last gene of strain 2 to transfer in the 20 minutes of conjugation time. How many minutes of conjugation time would be needed to allow the next gene on the map to transfer from Hfr strain 2?

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.

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.