Recombinant DNA:

Recombinant DNA refers to a molecule that has been created by combining DNA from two different sources, typically from different species. This process involves the isolation and manipulation of specific DNA segments, resulting in the creation of a new DNA molecule with a combination of genetic material from different organisms.

The Answer:

The correct answer is option 'B': DNA with a piece of foreign DNA. This is because recombinant DNA is formed by the insertion of a foreign DNA fragment into a vector, which is typically a plasmid or a viral genome. The foreign DNA fragment can be obtained from any organism, and it is introduced into the vector through a process called DNA cloning.

Explanation:

Recombinant DNA technology has revolutionized the field of molecular biology and has numerous applications in research, medicine, agriculture, and industry. The process of creating recombinant DNA involves several steps:

1. Isolation of DNA: DNA is extracted from the organism of interest, which can be a virus, bacterium, plant, or animal.

2. Selection of Vector: A vector is chosen to carry the foreign DNA fragment. Vectors are usually small, self-replicating DNA molecules, such as plasmids or viral genomes, that can be easily manipulated in the laboratory.

3. Insertion of Foreign DNA: The foreign DNA fragment is inserted into the vector. This is often done by using restriction enzymes, which can cut DNA at specific sites. The vector and the foreign DNA are cut with the same restriction enzyme, resulting in complementary sticky ends that can be easily joined together.

4. Ligation: The vector and the foreign DNA are joined together using an enzyme called DNA ligase. This creates a recombinant DNA molecule, with the foreign DNA fragment integrated into the vector.

5. Transformation: The recombinant DNA molecule is introduced into a host organism, such as bacteria or yeast. This is typically done by a process called transformation, where the host cells are made competent to take up the recombinant DNA.

6. Selection and Expression: The transformed host cells are then selected based on the presence of a selectable marker, which is often included in the vector. This marker allows for the identification and isolation of cells that have successfully taken up the recombinant DNA.

In conclusion, recombinant DNA refers to a DNA molecule that has been created by combining DNA from two different sources. The foreign DNA fragment is inserted into a vector, resulting in the formation of a new DNA molecule with a combination of genetic material from different organisms.