Final answer:
In bacteria, the DNA sequence comprising multiple genes controlled by a single promoter is known as an operon, and the resultant mRNA is called polycistronic mRNA, so the answer is c. an operon, a polycistronic.
Step-by-step explanation:
In bacteria, the unit of DNA that contains multiple genes under the control of a single promoter is called an operon. The mRNA produced from this unit is referred to as polycistronic mRNA. So, the correct answer is c. an operon, a polycistronic. The operon includes a promoter, where RNA polymerase initiates transcription, and an operator, where regulatory proteins bind to control the transcription process. Genes within an operon are transcribed into a single mRNA molecule called polycistronic because it can encode more than one polypeptide or protein, allowing for coordinated regulation of genes encoding proteins with related functions.