D. Things that are kept constant.
Controls are used in an experiment where some variable is being changed. By only changing one thing and keeping the others constant they can make sure that any change in the results is caused by the variable and not the constant, since the constant didn’t change.
D. All 3..................................
It is likely that the light blue colonies have a mutation in GENE I (lacI gene). LacI (lactose inhibitor) is a DNA-binding factor that represses transcription of the lac operon.
The lacI gene (regulatory gene for lac operon) is a gene located upstream of the three genes of the lac operon (i.e., lacZ, lacY, and lacA), which are transcribed as a unit.
The inducer of the lac operon is allolactose. When lactose is present, a small amount of this molecule is converted to allolactose.
The lac repressor, which is encoded by the lacI gene, binds to the operator upstream of the lac operon, thereby preventing its transcription unless the inducer is present.
Finally, the lacZ gene produces an enzyme called β-galactosidase, while X-gal is a blue-colored product precipitated when a bacterial colony expresses a functional β-galactosidase.
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