An Hfr strain with the genotype cys+ pro+ gly+ str+ is mated with an F- strain c

Question

An Hfr strain with the genotype cys+ pro+ gly+ str+ is mated with an F- strain carrying the genotype cys- pro- gly- str- . In an interrupted mating experiment, small samples of the conjugating bacteria are withdrawn every 3 minutes for 30 minutes. The withdrawn cells are shaken vigorously to stop conjugation and then placed on three different selection media, composed as follows: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 proline, glycine, and streptomycin
Medium 2: Minimal medium plus cysteine, glycine, and streptomycin
Medium 3: Minimal medium plus cysteine, proline, and streptomycin

What donor gene is the selected marker in each medium?

Medium 1

Medium 2

Medium 3

cysteine

proline

glycine

I chose A, B, C

Use this Question for the following questions:

Using the information in the question above, which of the following bacteria can grow in Medium 1? Check all that apply.

cys+ pro- gly+ str+

cys- pro- gly+ str+

cys- pro+ gly+ str+

cys- pro+ gly- str+

cys+ pro+ gly+ str+

cys+ pro+ gly- str+

cys- pro- gly- str+

cys+ pro- gly- str+

Again use the information in the 2 questions above. The table below shows the number of colonies growing on each selection medium. The sampling time indicates how many minutes have passed since conjugation began. Determine the order of donor genes pro, leu and met.

gly, cys, pro

gly, pro, cys

pro, gly , cys

cys, pro, gly

cys, gly, pro

pro, cys, gly

Medium 1

Medium 2

Medium 3

A.

cysteine

B.

proline

C.

glycine

# Colonies Sampling Time min Plate 3 0 0 0 0 0 62 85 Plate 2 Plate 1 0 0 0 0 51 79 109 144 0 12 15 18 21 24 62 87 124 210 250 250

Explanation / Answer

1.Selected marker gene for each medium will the one that is not present in the medium. One that the cell is expected to synthesize if genes are transferred from F+ station to F-strain.

So accordingly,

1

2.

3.

2.Following Bacteria can grow in medium 1 :- ( they must have cysteine residue in them, as medium 1 does not have cysteine in it)

cys+pro- gly+ str+

cys+pro+ gly + str+

cys+pro+gly-str+

cys+pro-gly-str+

3. Order of donor genes. The marker gene that would first appear in the medium in which it's originally absent , will be the first gene on time map.and so on for 2nd and 3rd gene. The order is:- proline cysteine glycine.

Medium marker gene

1

cysteine

2.

Proline

3.

glycine

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