202hw7KEY - Biology 202 Homework 7 KEY Due: 10/30 or 10/31;...

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Biology 202 Homework 7 KEY Due: 10/30 or 10/31; in discussion 1. Hfr strains chosen for use in conjugation studies have the locus that controls antibiotic resistance at a site very distant from the F factor insertion site. Why is such a location for the gene critical to the design of the experiment? Answer: (1pt ) Antibiotics are often used to select against the donor strain so that only recipient strains that have received certain genes from the donor strain can grow on selective media following conjugation. The donor strain is then sensitive to the antibiotic used and the recipient strain is resistant. The selective media that are used to test if certain genes have been transferred to the recipient strain contain the antibiotic. When the sensitive version of the antibiotic resistance gene has been transferred from the donor to the recipient, the recipients fail to grow on the selective media. Therefore the antibiotic resistance gene (for which the donor has the sensitive allele) should be far away from the insertion site so that it is transferred late in the process. 2. If leu + str R recombinants are desired from the cross Hfr leu str S X F - leu - str R , on what kind of medium should the recombinants be grown for identification? Answer: (1 pt) Minimal medium with streptomycin. Minimal so that only leu+ cells grow and with streptomycin so that only streptomycin resistant cells grow. 3. Five Hfr strains A through E are derived from a single F + strain of E. coli . The following chart shows the entry times (minutes) of the first five markers into an F - strain when each is used in an interrupted-conjugation experiment: A B C D E mal + (1) ade + (13) pro + (3) pro + (10) his + (7) str S (11) his + (28) met
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This note was uploaded on 01/29/2009 for the course BIOL 202 taught by Professor Staff during the Spring '08 term at New Mexico.

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202hw7KEY - Biology 202 Homework 7 KEY Due: 10/30 or 10/31;...

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