Final answer:
The DNA segment that must be adjacent to the gene(s) it regulates is called an enhancer. Enhancers are cis-acting elements that bind to transcription factors and play a crucial role in regulating gene expression.
Step-by-step explanation:
The DNA segment that must be adjacent to the gene(s) it regulates is called an enhancer. Enhancers are cis-acting elements that bind to transcription factors and play a crucial role in regulating gene expression. They can be located either proximal or distal to the promoter of a gene. Enhancers contain short DNA sequences called distal control elements, and when activators bind to these elements, they interact with mediator proteins and transcription factors to promote transcription.