In: Biology
or each of the E. coli strains containing the lac operon alleles listed, indicate whether beta-galactosidase and permease will be synthesized or not (type yes or no)
Genotype |
Beta-galactosidase |
Permease |
||
Lactose present |
Lactose absent |
Lactose present |
Lactose absent |
|
I+ P+ O+ Z- Y+ / I+ P+ Oc Z+ Y+ |
||||
I+ P+ O+ Z+ Y+ / I- P+ O+ Z+ Y- |
||||
I- P- O+ Z+ Y- / I+ P+ Oc Z- Y+ |
||||
Is P+ O+ Z+ Y+ / I- P+ O+ Z+ Y- |
Ans:
Genotype |
Beta-galactosidase |
Permease |
||
Lactose present |
Lactose absent |
Lactose present |
Lactose absent |
|
I+ P+ O+ Z- Y+ / I+ P+ Oc Z+ Y+ |
Yes |
Yes |
Yes |
Yes |
I+ P+ O+ Z+ Y+ / I- P+ O+ Z+ Y- |
Yes |
No |
Yes |
No |
I- P- O+ Z+ Y- / I+ P+ Oc Z- Y+ |
No |
No |
Yes |
Yes |
Is P+ O+ Z+ Y+ / I- P+ O+ Z+ Y- |
No |
No |
No |
No |
Explanation: In first partial merozygotes, functional repressor protein (lacI+) unable binds the non functional operator (lacOc). So, the merozygotes produce both beta-galactosidase and permease in the presence or absence of lactose because functional beta-galactosidase (lacZ+) and permease (lacY+) genes are present with functional promoter (lacP+) and nonfunctional operator.
In second partial merozygotes, functional repressor protein (lacI+) binds to the functional operator (lacO+) in both the haploid because lacI+ is trans-acting. So, the merozygotes does not produce beta-galactosidase and permease in the absence of lactose but produces in the presence of lactose with functional beta-galactosidase (lacZ+), permease (lacY+) promoter (lacP+) genes because the inducer lactose binds to repressor protein.
In third partial merozygotes, functional repressor protein (lacI+) unable to binds to the nonfunctional operator (lacOc) in the 2nd haploid. So, the merozygotes produces permease in the absence and presence of lactose (presence of functional lacY+) but does not produces beta-galactosidase both in the presence and absence of lactose because promoter (lacP-) is non functional (RNA polymerase unable to binds) in 1st haploid where functional beta-galactosidase gene is present and nonfunctional beta-galactosidase gene (lacZ-) is present in 2nd haploid.
In fourth partial merozygotes, the trans-acting super-repressor (lacIs) is present that can binds to both functional operator (lacO+). So, the merozygotes does not produces beta-galactosidase and permease in the absence and presence of lactose because the super repressor cannot binds to inducer lactose in the presence of lactose.