Gene cloning involves the replication of DNA fragments in host organisms to produce identical copies. It serves as a vital tool for the production of proteins, vaccines, and therapeutic treatments. On the other hand, rDNA libraries—systematic collections of cloned DNA sequences—function as extensive genomic and cDNA archives. Genomic libraries store all the genetic material from an organism, encompassing both coding and non-coding regions, while cDNA libraries represent the expressed genes, providing insights into active gene expression at specific times or conditions. These genetic toolkits allow scientists to identify, isolate, and study disease-causing mutations.