Final answer:
A plasmid is a small circle of double-stranded DNA used as a cloning vector, separate from a cell's chromosome, serving as an important tool for gene cloning and expression studies. option a.
Step-by-step explanation:
A common type of cloning vector is a plasmid, which is a small circle of double-stranded DNA separate from the cell's chromosome. The correct answer to the fill-in-the-blank question is a) Plasmid.
In the context of molecular cloning, a plasmid is a small, circular, extrachromosomal DNA molecule that is independent of the cell's chromosomal DNA and can replicate on its own.
These plasmids can be transferred from one bacterium to another, allowing for the exchange of genetic material such as antibiotic resistance. Plasmids serve as important tools in biotechnology and research, functioning as vectors to insert foreign DNA into host cells for cloning and gene expression studies.
Option a.