Which of the following describes cDNA accurately?

cDNA, or complementary DNA, is synthesized from messenger RNA (mRNA) through a process known as reverse transcription. This process involves using the enzyme reverse transcriptase to create a DNA strand that is complementary to the mRNA template. As a result, cDNA represents only the coding sequences of the genes that are actively expressed in a particular cell or tissue at a given time, reflecting the mRNA transcripts that were present.

Considering the other options, they do not accurately describe cDNA. cDNA does not include all coding and noncoding regions, as it specifically corresponds to the segments of DNA that are transcribed into mRNA, typically excluding introns and noncoding regions. It is not composed entirely of regulatory regions; rather, it primarily reflects the coding sequences of genes. Lastly, cDNA is not used for sequencing entire genomes. Instead, it is primarily used in gene expression studies, cloning, and other applications that focus on specific mRNA populations.