The correct answer is codominance. According to this mode of inheritance, individuals that are heterozygous for a condition express both alleles equally. If the offspring were exhibited incomplete dominance, their phenotype would have been a red-green blend because the heterozygous condition is a blend of both alleles. Complete dominance occurs when the heterozygous condition exhibits the same phenotype as the homozygous dominant. In epistasis, the expression of one gene is dependent on the expression of a second, which is a form of inheritance that does not apply to this question. Finally, a polygenic trait is a trait that is conferred by multiple genes, a situation for which we know is not the case in this question. 

Since A and B can be expressed at the same time on a red blood cell, we can say that A and B are codominant to one another. On the other hand, this cannot be said for the O allele. If a person has an A allele and an O allele, that person will have type A blood. Both A and B are dominant over O. As a result, we also see complete dominance take place with blood types. To help solidify this concept, added below is a genotype/phentoype comparison:

A/A = A blood

A/O = A blood

O/O = O blood

B/B = B blood

B/O = B blood

A/B = AB blood

Activation of the lac operon is necessary for the transport and metabolism of lactose sugars by E. coli. Lactose sugars actively work to remove a repressor that statically inhibits transcription; however, high concentrations of glucose (and, thus, low concentrations of cAMP) will prevent these genes from being transcribed rigorously. In order for the lac operon to be active at high levels, lactose must be present and glucose must be absent.

The lac operon is a system designed to only express particular proteins when the concentration of glucose is low and the concentration of lactose is high. The common cellular response to a low concentration of glucose is to increase the concentration of cAMP in order to activate various alternative metabolic pathways. Both a high concentration of cAMP and a high concentration of lactose are necessary to get sustained expression of the lac operon. When glucose levels begin to rise, the cAMP concentration will begin to fall and the operon function will deteriorate.

lac I is the gene that encodes for the repressor of the lac operon. If there is no repressor, the cell will constantly express the genes present in the lac operon whether or not the typical conditions are present.

A mutation of the gene encoding -galactosidase permease (lac Y) would prevent lactose from entering the cell. A mutation in the gene encoding -galactosidase (lac Z) would prevent the breakdown of lactose. A mutation in the promoter region would prevent RNA polymerase from binding.

Prokaryotic organisms often have functionally related genes joined together on the chromosome under the direction of a single promoter. These structures are called operons. Operons have additional sequences, called operators that can be bound by either repressor or activator proteins, which will repress or activate transcription of the operon. One commonly studied example is the lac operon, whose genes encodes products required for lactose metabolism.

Negatively regulated operons that are said to be inducible have their operator sequence bound by a repressor molecule normally. That leads to these operons being off normally. For these operons to be turned on and transcribed, a small molecule called an inducer has to bind to and inactivate the repressor protein.

Promoters are the sites where transcription factors and RNA polymerase bind to initiate transcription. It makes sense that the promoter would be found upstream of a gene (i.e. before a gene). "Downstream of the coding region" and "in the middle of the coding region" are redundant answers, and neither describes a location where a promoter would normally be located. The 3' UTR describes a region of mRNA and, thus, has nothing to do with promoters.

As the name suggests, enhancers enhance the expression of a gene; they increase the number of mRNA transcripts produced from said gene. Silencers do the opposite, and repress the expression of a gene by serving as a binding site for repressors. It does not matter exactly how far enhancers are from the gene (either upstream or downstream) as long as they are geometrically close.

Bacterial RNA polymerase is very similar to eukaryotic RNA Polymerase II in that both have many subunits and form a holoenzyme with cofactors. The rest of the answers are in fact unique to bacterial transcription.