A cross is made between the streptomycin -resistant (Str^2) F-strain marked with

Question

A cross is made between the streptomycin -resistant (Str^2) F-strain marked with the characters Gal T Ax^2 Lac Tl^R Mal Xyl L^- and the photographic Hfr strain having the opposite characters. After 60 minutes of contract samples are transferred to places with minimal medium plus streptomycin. All markers can be transferred within this time. Key to characters T and L are amino acids; Gal, Lac, Mal, Xyl are sugars; Az = azide; Tl is phage; Str = streptomycin. The original mixture is in the ratio of T + L + SR recombinants are as follows: 72% Tl^2, 0% Mal, 27% Gal, 91% Ar^3, 0% Xyl, 48% Lac. What is the counterselective agent that presents the Hfr individuals from obscuring the detection of recombinants? In that order are these genes probably being transmitted by the Hfr? (T + L + must come in first, and they mast be closely linked.) What is the meaning of 0% Mal + and 0% Xyl + ? Where do you think there markers are tented an the chromosome relative to Str R?

Explanation / Answer

The counterselcetive agent for outing the Hfr strains will be no azide and Phage particles presence. It is because Hfr strains are T1 phage sensitive and cannot grow in azide absent while the recombinants can grow because they have resistant power for T1 phage.

The order of transferring of genes will follow according the frequencies provided. High frequency substance will enter first. So the gene order is: L+--- Lac+---Gal+. The sensitive genes are absent in Hfr strain

0%Mal and Xyl is representing that genes are present at ori region of plasmid and that’s why they cannot be transferred.

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