In a cotransformation experiment (see solved problem S4), DNA was isolated from a donor strain that was proA+ and srrC+ and sensitive to tetracycline. (The proA and strC genes confer the ability to synthesize proline and confer streptomycin resistance, respectively.) A recipient strain is proA- and srrC- and is resistant to tetracycline. After transformation, the bacteria were first streaked on a medium containing proline, streptomycin, and tetracycline. Colonies were then restreaked on a medium containing streptomycin and tetracycline. (Each type of medium had carbon and nitrogen sources for growth.) The following results were obtained:
70 colonies grew on the medium containing proline, streptomycin, and tetracycline, but only 2 of these 70 colonies grew when restreaked on the medium containing strepto’mycin and tetracycline but lacking proline.
A. If we assume the average size of the DNA fragments is 2 minutes, how far apart are these two genes?
B. What would you expect the cotransformation frequency to be if the average size of the DNA fragments was 4 minutes and the two genes are 1.4 minutes apart?
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