iGenetics 3rd Edition by Peter Russell

Exercise 2

The growing resistance of bacteria to antibiotics is a significant health concern. As early as the 1950s, physicians identified hospital patients afflicted with severe diarrhea, resulting from bacterial dysentery, who did not respond to previously effective antibiotics. Some strains of Shigella, the pathogen that causes bacterial dysentery, had developed resistance to antibiotics. In the 1970s the basis for this resistance was discovered: plasmids containing multiple antibiotic resistance genes were isolated from Shigella. Researchers then found that the same genes conferring antibiotic resistance in Shigella were also present in other species of pathogenic bacteria.
a. In each of the following crosses, where would genes conferring antibiotic resistance need to be located in order for them to be transferred reliably from one bacterial cell to another cell?
i. Hfr (resistant) × F - (sensitive)ii. F + (resistant) × F - (sensitive)b. Which cross would be more efficient at spreading antibiotic resistance between cells? Why?
c. That the same genes conferring resistance in Shigella were found in other bacterial species suggests thatthese genes were transferred across species. Generatehypotheses to explain how this might have occurred.