GenCh10answers - 1. The I gene determines the synthesis of...

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1. The I gene determines the synthesis of a repressor molecule, which blocks expression of the lac operon and which is inactivated by the inducer. The presence of the repressor I + will be dominant to the absence of a repressor I . I s mutants are unresponsive to an inducer. For this reason, the gene product cannot be stopped from interacting with the operator and blocking the lac operon. Therefore, I s is dominant to I + . 2. O c mutants are changes in the DNA sequence of the operator that impair the binding of the lac repressor. Therefore, the lac operon associated with the O c operator cannot be turned off. Because an operator controls only the genes on the same DNA strand, it is cis (on the same strand) and dominant (cannot be turned off). 3. a. You are told that a , b , and c represent lacI , lacO , and lacZ , but you do not know which is which. Both a and c have constitutive phenotypes (lines 1 and 2) and therefore must represent mutations in either the operator ( lacO ) or the repressor ( lac I ). b (line 3) shows no ß-gal activity and by elimination must represent the
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This note was uploaded on 09/25/2010 for the course BIOL 3301 taught by Professor Gunaratne during the Fall '05 term at University of Houston.

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GenCh10answers - 1. The I gene determines the synthesis of...

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