You Have Isolated Two Mutations Linked to the Lac Operon

question 19

Essay

You have isolated two mutations linked to the lac operon, which you designate Lac1^- and Lac2^- that cause constitutive expression of the operon. You construct strains carrying a lac operon with a mutant lacY gene on an F'. You test both ß-galactosidase activity and Lac permease activity in the strains you constructed using the artificial inducer IPTG. $$\begin{array}{l}~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\text { B-galactosidase activity Lac permease activity }\\\begin{array} { ccccc } & \text { - IPTG}&{+ IPTG } & \text { - IPTG } & \text { + IPTG } \\\mathrm { Lac1 } ^ { - } \operatorname { lac } Z^- \operatorname { lac } Y ^ { + } / \mathrm { F } ^ { \prime } \operatorname { lac } Z ^ { + } \operatorname { lac } Y ^ { - } & - & + & + & + \\\mathrm { Lac2 } ^ { - } \operatorname { lac } Z^- \operatorname { lac } Y ^ { + } / \mathrm { F } ^ { \prime } \operatorname { lac } Z ^ { + } \operatorname { lac } Y ^ { - } & + & + & + & +\end{array}\end{array}$$ Are Lac1^- and Lac2^- dominant or recessive? Do they act in cis or in trans? Indicate how you can determine both of these properties for each mutation. What type of lac mutations best fit the properties of Lac1^- and of Lac2^-?

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