A clone is an exact copy of an organism, organ, single cell, organelle or macromolecule. Cell lines for medical research are derived from a single cell allowed to replicate millions of times, producing masses of identical clones.
Gene cloning is the act of making copies of a single gene. Creating millions of copies helps us visualize genes using methods like electrophoresis, which helps us determine the size of the gene. Cloning also helps us characterize factors affecting transcription and translation, and study the gene product, because we are able to create transgenic organisms to overexpress the gene (make lots of copies of the protein product). Once the gene product is characterized, clones of the gene can be used to control the molecular pathways in which they are involved, which can be useful in many areas of biomedical and industrial research.