The genes shown in the table are from the lac operon system of E. coli. The symb
ID: 166858 • Letter: T
Question
The genes shown in the table are from the lac operon system of E. coli. The symbols a, b, and c represent the repressor (I) gene, the operator (O) region, and the structural gene (Z) for beta-galactosidase, although not necessarily in that order. Furthermore, the order in which the symbols are written in the genotypes is not necessarily the actual sequence in the lac operon.
Activity (+) or inactivity (-) of Z gene.
Genotype
Inducer absent
Inducer present
a-b+c-
-
-
a+b-c+
+
+
a+b+c-
+
+
a+b-c+/a-b+c-
+
+
a+b+c+/a-b-c-
-
+
a+b+c-/a-b-c+
-
+
a-b+c+/a+b-c+
+
+
A) Which symbol (a, b, or c) represents each of the lac genes (I, O, and Z). B) For each symbol, write one or two sentences explaining how your model is consistent with the data.
Genotype
Inducer absent
Inducer present
a-b+c-
-
-
a+b-c+
+
+
a+b+c-
+
+
a+b-c+/a-b+c-
+
+
a+b+c+/a-b-c-
-
+
a+b+c-/a-b-c+
-
+
a-b+c+/a+b-c+
+
+
Explanation / Answer
From the above data given for the Lac operon In E.coli,
The symbol, "a" represents Structural gene (Z), "b" represents Repressor gene (I) and "c" represents Operator gene(O) of lac genes.
In the first genotype (a-b+c- or Z-I+O-) there is no activity of structural ad operator gene eventhough the repressor gene is active.So no betagalactosidase produced in the presence and absence of inducer.
In genotype (a+b-c+ or Z+I-O+),due to the inactive repressor gene,the operator gene will be free from repressor protein so threre is a production of betagalactosidase in the presence and absence of inducer.
In the genotype (a+b+c- or Z+I+O-),due to the in active operator, the repressor which is produced by the repressor gene can not inhibits the activity of the structural genes, so threre is a production of betagalactosidase in the presence and absence of inducer.
These explanations strongly supports the data.
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