You are working with two strains of E. coli in the lab. Neither strain will grow

Question

You are working with two strains of E. coli in the lab. Neither strain will grow on minimal media (MM,

media not supplemented with amino acids). Strain 1 will grow on media supplemented with threonine

but not histidine. Strain 2 will grow on media supplemented with histidine but not threonine. You mix

the two strains together and let them grow for a while in complete media (containing both

supplemental threonine and histidine), and after a few hours, you re-isolate each strain and test its

ability to grow on MM, MM + his, and MM + thr. The results of your experiment are summarized in the figure above.

PLEASE ANSWER ALL QUESTIONS:

A) Using the nomenclature thr+, thr-, his+, his-, give the genotype of each original strain:

Strain 1:

Strain 2:

B) You suspect that the new phenotype in strain 2 is a result of conjugation. Which strain would be

considered an Hfr strain at the start of conjugation?

C) Which strain initiated the conjugation event?

D) Explain why the phenotype of strain 1 was unchanged.

E) Which of the following is the most likely genotype of the “new” strain 2? Explain your answer

a. his+; thr-

b. his+/his-; thr+/thr-

c. his-;thr-

d. his+; thr+

e. his+/his-; thr+

f. his+; thr+/thr-

g. his-; thr+/thr-

QUESTION: You are working with two strains of E. coli in the lab. Neither strain will grow on minimal media (MM, media not supplemented with amino acids). Strain 1 will grow on media supplemented with threonine but not histidine. Strain 2 will grow on media supplemented with histidine but not threonine. You mix the two strains together and let them grow for a while in complete media (containing both supplemental threonine and histidine), and after a few hours, you re-isolate each strain and test its ability to grow on MM, MM+ his, and MM+ thr. The results of your experiment are summarized below Minimal Media (MM)MM+his MM+ thr Strain 1 (before) No Growth Strain 2 (before) Strain 1 (after) No Growth No Growth Growth No Growth Growth No Growth Growth Growth No Growth Growth Growth Strain 2 (after)

Explanation / Answer

Ans-A- the genotype of the original strains will be

Strain 1= thr+; his-

Strain2= his+; thr-

Ans-b- strain 1 will be considered as hfr because strain 1 is the strain which integrate it's gene into host cells.

Ans-C- the gene of hfr are isolated to make a clone so the strain with hfr is considered to start the conjugation.

Ans-D- because during conjugation strain 1 act as a donor and not as a recipient due to which it does not gain any external genetic material and remain unchanged.

Ans-e- the possible genotype of strain 2 after conjugation will be his+; the+ . It means option d is correct.

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