The following table shows several bacterial strain lac operon genotypes (some ar
ID: 7434 • Letter: T
Question
The following table shows several bacterial strain lac operon genotypes (some are partial diploids).
a) Fill in the blanks in the “lactose absent” and “lactose present” columns in this table. (+) means significant levels of active ß-galactosidase enzyme can be detected. (–) means no significant levels of active ß-galactosidase enzyme. The first line is filled in for reference.
Strain genotype
Lactose absent
Lactose present
1. lacI+ lacP+ lacO+ lacZ+ lacY+
2. lacI+ lacP+ lacOc lacZ+ lacY+
3. lacI+ lacP+ lacOc lacZ–lacY+
4. lacIs lacP+ lacOc lacZ+ lacY+
5. lacI–lacP+ lacO+ lacZ+ lacY+ / lacI+
6. lacIs lacP+ lacO+ lacZ+ lacY+/ lac I+
b) If lactose is absent and glucose is present in the culture medium of strain 4, will significant levels of active ß-galactosidase enzyme be detected? Explain… in brief, just because there is lots of room left, you don’t need to fill it.
Strain genotype
Lactose absent
Lactose present
1. lacI+ lacP+ lacO+ lacZ+ lacY+
2. lacI+ lacP+ lacOc lacZ+ lacY+
3. lacI+ lacP+ lacOc lacZ–lacY+
4. lacIs lacP+ lacOc lacZ+ lacY+
5. lacI–lacP+ lacO+ lacZ+ lacY+ / lacI+
6. lacIs lacP+ lacO+ lacZ+ lacY+/ lac I+
Explanation / Answer
(a) first strain - lactose present
second strain - lactose present
third strain - lactose present but lacZ gene is not expressed. lacY gene is expressed.So lactose is not broken down into glucose and galactose
fourth strain - lactose present
fifth strain - lactose present
sixth strain - lactose present
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