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

Among the mechanisms of gene transfer in bacteria, which one is capable of transferring the largest chromosome segment from donor to recipient? Which process generally transfers the smallest donor segments to the recipient? Explain your reasoning for both answers.

Explain the observations that led Zinder and Lederberg to conclude that the prototrophs recovered in their transduction experiments were not the result of F⁺ mediated conjugation.

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

Draw a consolidated map of the bacterial chromosome. (Hint: Begin by placing the insertion site for Hfr A at the 2 o'clock position and arranging the genes thr–leu–azi- . . . in clockwise order.)

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.

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

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

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.