(a) Define recombinant DNA. (b) Explain their role in genetic engineering.

(a) Recombinant DNA refers to the process of combining DNA molecules from distinct sources, resulting in a genetically modified sequence. This process typically involves cutting and splicing DNA fragments using enzymes, such as restriction endonucleases and DNA ligases, in order to construct new genetic sequences with desired traits. (b) Recombinant DNA plays a central role in genetic engineering, wherein scientists manipulate genes in order to produce desired traits in organisms. This technique allows scientists to introduce new genetic material into an organism or to modify existing genetic material, leading to the development of new strains of plants, animals, and microorganisms with improved characteristics. For example, genetic engineering has been used to produce crops with increased resistance to pests and environmental stressors, as well as bacteria that can be used to clean up environmental pollutants. Recombinant DNA techniques also have important applications in medicine, such as the development of genetically modified vaccines and gene therapies for inherited diseases.