The circular order of genes on the E. coli chromosome is *A B C D E F G H*, with the * indicating that the ends of the chromosome are attached to each other. Two copies of an IS element are located in this chromosome: one between genes C and D, and the other between genes D and E. A single copy of this element is also present in the F plasmid. Two Hfr strains were obtained by selecting for integration of the F plasmid into the chromosome. During conjugation, one strain transfers the chromosomal genes in the order D E F G H A B C, whereas the other transfers them in the order D C B A H G F E. Explain the origin of these two Hfr strains. Why do they transfer genes in different orders? Does the order of transfer reveal anything about the orientation of the IS elements in the E. coli chromosome?