You are hereForums / USMLE Forums / Usmle Step 1 / A tetracycline-sensitive Trp- and His- auxotroph E.coli
A tetracycline-sensitive Trp- and His- auxotroph E.coli
A tetracycline-sensitive (tet +), Trp- and His- auxotroph E. coli is mixed in equal proportions with tetracycline-resistant (tet -)prototroph of the same species in medium containing Trp, His and DNAase. Later, the culture was seeded in media with different combinations of tetracycline, Trp and His.
The resultant colonies:
1) Prototrophic in 70%;
2) Auxotrophic - 30%, of whom 60% required Trp and 40% - both Trp and His.
Which of the folllowing conclusions concerning the three genes involved in this experiment is supported by the data?
A. All tet- bacteria derived from the original prototrophs;
B. The His gene is closer to the tet-resistance gene than the trp-gene;
C. Transmission of genes from prototrophs to auxotrophs involved transformation;
D. The Trp and His genes are very closely located;
E. The Trp gene is the one closest to the origin of replication (Ori)
The resultant colonies:
1) Prototrophic in 70%;
2) Auxotrophic - 30%, of whom 60% required Trp and 40% - both Trp and His.
Which of the folllowing conclusions concerning the three genes involved in this experiment is supported by the data?
A. All tet- bacteria derived from the original prototrophs;
B. The His gene is closer to the tet-resistance gene than the trp-gene;
C. Transmission of genes from prototrophs to auxotrophs involved transformation;
D. The Trp and His genes are very closely located;
E. The Trp gene is the one closest to the origin of replication (Ori)
Tags
. [url=http://www.insurance-top.com]cars insurance[/url] from website .
. from website .
The resultant colonies:
1) Prototrophic in 70%;
2) Auxotrophic - 30%, of whom 60% required Trp and 40% - both Trp and His.
Which of the folllowing conclusions concerning the three genes involved in this experiment is supported by the data?
A. All tet- bacteria derived from the original prototrophs;
B. The His gene is closer to the tet-resistance gene than the trp-gene;
C. Transmission of genes from prototrophs to auxotrophs involved transformation;
D. The Trp and His genes are very closely located;
E. The Trp gene is the one closest to the origin of replication (Ori)[/quote] The answer is C - by transformation. It seems so because there has to be some sort of genetic transfer between the 2 strains to show such results. Also the genes and origin of replication theory mentioned in most of the choices is not pluasible because once you have transcription of DNA all genes will be transcribed irrespective of distance between them or from ori. But for this transcription to occur the tet- gene has to be passed on to the tet+ starin by some method. Hence C.