In E . coli the following four Hfr strains donate the markers shown below in the

Question

In E. coli the following four Hfr strains donate the markers shown below in the orders (left to right) given:

                 Hfr strain           Order of gene transfer

                        1                      G S R O C

                        2                      O C K B U

                        3                      G U B K C

                        4                      U G S R O

All the Hfr strains were obtained from the same F+ strain. What is the gene order on the original F+ chromosome? Draw a linear map and start at B just for consistency

Explanation / Answer

Gene order:

Hfr strain 2 shows that B has U and K as its immediate markers. It also shows the gene order KCO.

Hfr strain 3 shows that U has G and B as immediate neighboring markers.

So,

Gene order is,

O-C-K-B-U-G-S-R

Gene order starting with B is,

B-U-G-S-R-O-C-K

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