Cloning is a process used to create an exact genetic replica of another cell, tissue, or organism. The copied material, which has the same genetic makeup as the original, is referred to as a clone. Cloning can occur naturally, such as in the case of identical twins, or it can be done in a lab. There are three different types of cloning:

• Gene cloning: This creates copies of genes or segments of DNA. Researchers use this technique to make copies of genes that they wish to study. The procedure consists of inserting a gene from one organism, often referred to as "foreign DNA," into the genetic material of a carrier called a vector.

• Reproductive cloning: This creates copies of whole animals. Reproductive cloning was originally carried out by artificial “twinning,” or embryo splitting, which was first performed on a salamander embryo in the early 1900s by German embryologist Hans Spemann. Later, scientists used a technique called nuclear transfer to create Dolly the sheep, the first mammal cloned from an adult cell.

• Therapeutic cloning: This creates embryonic stem cells for experiments aimed at creating tissues to replace injured or diseased tissues. Researchers hope to use these cells to grow healthy tissue to replace injured or diseased tissues in the human body.

Cloning can be used in biomedical research to duplicate any kind of biological material for scientific study, such as a piece of DNA or an individual cell. However, the type of cloning that is the focus of much ethical controversy involves the generation of cloned embryos, particularly those of humans, which are genetically identical to the organisms from which they are derived, and the subsequent use of these embryos for research, therapeutic, or reproductive purposes.