3) (from a previous final) A partial diploid was generated by transforming E. co

Question

3) (from a previous final) A partial diploid was generated by transforming E. coli with a plasmid containing lacI, the promoter and operator for the lac operon, and the lac operon. The genotypes of the partial diploid mutants with respect to the lac operon are shown below. +, indicates wild-type, -, indicates mutant, c represents constitutive, s represents no binding to inducer, i represents lacI, p represents the lac operon promoter, o represents the lac operon operator, z represents lacZ, y represents lacY, and a represents lacA.

Which strain(s) will show the listed phenotypes? If no strain will show the phenotype, please indicate as “none”.

I. constitutive production of b-galatosidase, but normal production of permease and transacetylase. ___________

II. super-repression of the lac operon ________

III. constitutive expression of the three genes within the lac operon ___________

Explanation / Answer

I. constitutive production of b-galatosidase, but normal production of permease and transacetylase. ___________
The answer is 3.

The operator has normal one and z is mutant one, under normal conditions the genes permease and transacetylase will be produced. As the operator is constitute in second operon of this merozygote the z gene expressed continously.

II. super-repression of the lac operon ________
The answer is None.

The superrepressor is present on 2nd genotype, but as the operator is constitutive in second operon, the gene z will be expressed continously.

III. constitutive expression of the three genes within the lac operon ___________
The answer is 1.

As the first genotype has a constitutive operator the genes will be expressed continously.

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