Final answer:
A genomic library contains promoter and enhancer sequences, whereas a cDNA library, created from mRNA to reflect expressed genes, does not include these regulatory elements.
Step-by-step explanation:
The genomic library has promoter and enhancer sequences present. The genomic library is constructed by cleaving an organism's complete genomic DNA into fragments and cloning them into vectors, such as cosmids. This type of library includes not only the expressed genes but also the intronic sequences and regulatory elements like promoters and enhancers that control gene expression.
Enhancers are sequences containing distal control elements to which activators bind, interacting with mediator proteins and transcription factors. Conversely, a cDNA library is created using the mRNA of the organism and reflects only the expressed genes. This means that a cDNA library lacks introns as well as promoters and enhancers which are non-coding DNA sequences that are not transcribed into mRNA.