What do you call an exact genetic copy of an organism or cell?

The term for an exact genetic copy of an organism or cell is "clone." Cloning refers to the process of creating a genetically identical copy of an organism, tissue, or cell. This can occur naturally, as in the case of identical twins, or artificially through methods such as somatic cell nuclear transfer, where the nucleus of a somatic cell is transferred into an egg cell that has had its nucleus removed. The result is a new organism or cell with the same genetic material as the original.

In contrast, gene therapy involves altering genes within an individual's cells to treat or prevent disease, stem cells can develop into various cell types and are not identical copies of an existing organism, and recombinant DNA refers to DNA molecules created by combining genetic material from different sources, which is not synonymous with creating an exact clone. Thus, "clone" specifically captures the essence of genetic identity, making it the correct choice.