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Investigating the negative regulation of the lac operon by allolactose, consider the following merozygote experiment: I...

Investigating the negative regulation of the lac operon by allolactose, consider the following merozygote experiment: I s O c Z + / F' I + O + Z +. Which statement correctly describes the regulation of ß-galactosidase synthesis in this merodiploid cell? Note that ß-galactosidase expression can come from either the chromosome or the plasmid.

Without lactose ß-galactosidase synthesis is ON; with lactose it is ON  

Without lactose ß-galactosidase synthesis is ON; with lactose it is OFF  

Without lactose ß-galactosidase synthesis is OFF; with lactose it is ON

Without lactose ß-galactosidase synthesis is OFF; with lactose it is OFF

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Answer #1

this cell has two lac operons one in the plasmid and the other in the chromosome.

I s O c Z + / F' I + O + Z +.

I s O c Z +, this operon has the gene for super repressor Is so super repressor is present in the cell, it cannot inhibit the expression of an operon with the normal operator even if lactose is present but it cannot inhibit the expression of an operon with the constitutive operator, so I s O c Z + this operon is expressed even if lactose is absent, that is in the cell Beta-galactosidase produced by lacZ gene expressed always.

a) Without lactose ß-galactosidase synthesis is ON; with lactose it is ON  

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