Question

The lac operon of E. coli encodes the two enzymes ß-Galactosidase and Permease. Indicate in the following table whether these enzymes are synthesized (“+”) or not (“–“) given the genotypes in the left column and the presence or absence of the inducer. Note that some of the genotypes are partial diploids, i.e. a second copy of the operon is present on a separate plasmid.

	Genotype	Inducer Absent		Inducer Present
		β-Galactosidase	Permease	β-Galactosidase	Permease
a)	I+P+O+Z+Y+
b)	I+P+O+Z–Y+
c)	I+P+O+Z+Y–
d)	I–P+O+Z+Y+
e)	Is P+O+Z+Y+
f)	I+P+Oc Z+Y+
g)	Is P+Oc Z+Y+
h)	I+P+Oc Z+Y–
i)	I–P+O+Z+Y+ I+P+O+Z–Y–
j)	I–P+O+Z+Y– I+P+O+Z–Y+
k)	Is P+O+Z+Y– I+P+O+Z–Y+
l)	I+P+Oc Z–Y+ I+P+O+Z+Y–
m)	I–P+Oc Z+Y– I+P+O+Z–Y+
n)	Is P+O+Z+Y– I+P+Oc Z–Y+
o)	I+P–Oc Z+Y– I+P+O+Z–Y+
p)	I+P–O+Z+Y– I+P+Oc Z–Y+
q)	I–P–O+Z+Y+ I+P+O+Z–Y–
r)	I–P+O+Z+Y– I+P–O+Z–Y+

Answer 1

The mutations are as follows;

P- =can't bind in RNA polymerase, results in uninducible mutant

I- =produces no functional repressor, results in constitutive expression of lac operon.

Oc =doesn't allow binding of repressor, constitutive in nature

Is =produces super repressor molecule, uninducible in nature

Z- =doesn't produce functional beta-galactosidase enzyme

Y- =doesn't produce functional permease enzyme

Genotype Inducer Absent Inducer Present B- Permease B Permease Galactosidase Galactosidase a) I+P+O+Z+Y+ b) c) d) I+P+O+Z-Y+ I+P+O+Z+Y- 1-P+O+Z+Y+ + e) f) Is P+O+Z+Y+ I+P+Oc Z+Y+ ++ Is P+OcZ+Y+ g) h) I+P+OcZ+Y- i) 1-P+O+Z+Y+ I+P+O+Z-Y- 1-P+O+Z+Y- I+P+O+Z-Y+ j) Is P+O+Z+Y- I+P+O+Z-Y+ 1 I+P+OcZ-Y+ I+P+O+Z+Y- + m) 1-P+OcZ+Y- I+P+O+Z-Y+ + 11 + i + ' T n) Is P+O+Z+Y- I+P+OcZ-Y+ I+P-Oc Z+Y- I+P+O+Z-Y+ p) I+P-O+Z+Y- I+P+OcZ-Y+ q) 1-P-O+Z+Y+ I+P+O+Z-Y- 1-P+O+Z+Y- I+P-O+Z-Y+