Cloning is the process of creating a genetically identical copy of a biological entity, whether it is a gene, a single cell, or an entire organism. Artificial cloning has been a focus of scientific investigation for decades. These scientific efforts have led to the successful cloning of a diverse range of organisms, from livestock to cells with human genetic material.
The Pioneering Era of Mammalian Cloning
The modern era of cloning was defined by the development of Somatic Cell Nuclear Transfer (SCNT), a technique that allows a specialized body cell to be reprogrammed to create a new organism. SCNT involves taking the nucleus from a somatic cell and inserting it into an egg cell that has had its own nucleus removed. An electrical pulse then stimulates the reconstructed egg to begin dividing as if it were a fertilized embryo.
This methodology was famously proven with the birth of Dolly the sheep in 1996 at the Roslin Institute in Scotland. Dolly was the first mammal successfully cloned from an adult somatic cell. Prior successful cloning efforts had relied on cells taken from embryos, making Dolly’s creation a profound demonstration that adult cell DNA could be completely reset to a primitive, embryonic state.
Following Dolly’s breakthrough, SCNT was rapidly applied to other livestock and laboratory animals. Scientists successfully cloned species such as mice, cows, goats, and pigs, primarily for agricultural and biomedical research purposes. These subsequent clones established the technique as a functional method for replicating mammals. The ability to create genetically uniform animals has been used to study disease and to produce genetically modified livestock capable of manufacturing pharmaceuticals in their milk.
Cloning of Domestic and Endangered Species
The application of cloning technology quickly moved into the commercial and conservation sectors. Companies now offer the service of cloning companion animals, such as cats and dogs. Owners pursue this option to create a genetically identical copy of a beloved pet, though environmental factors mean the clone will not be an exact personality replica.
Cloning has also been explored as a tool for genetic preservation in conservation biology. One early success was the cloning of a gaur in 2001. Though the cloned calf died shortly after birth, the initial success demonstrated the feasibility of interspecies cloning using a domestic cow as a surrogate mother.
More recently, the technology has produced more viable results, such as the successful cloning of a Black-footed Ferret named Elizabeth Ann in 2020. This ferret was cloned from the frozen cells of an individual that died over three decades prior. This effort is significant because the clone introduces much-needed genetic diversity back into the severely bottlenecked population.
Non-Mammalian Animal and Plant Cloning
While mammalian cloning is the most widely recognized, successful cloning of non-mammalian vertebrates occurred decades earlier using simpler nuclear transfer methods. In the 1950s, scientists successfully cloned frogs by transferring the nucleus of a tadpole’s intestinal cell into an unfertilized egg. Later experiments also yielded clones of fish species.
Plant cloning, in contrast, is an ancient and common practice that does not rely on the complex SCNT process. Gardeners and agriculturists have long utilized methods like grafting and taking cuttings to produce plants that are genetically identical to the parent.
In modern agriculture, techniques like tissue culture and micropropagation allow for the rapid and large-scale replication of desirable plant varieties. A small piece of plant tissue is grown in a sterile, nutrient-rich medium to produce an entire, genetically identical plant. This allows for the mass production of disease-free crops and ornamental plants with consistent traits.
Creation of Cloned Human Cells and Embryos
Scientists have successfully applied the SCNT technique to create human embryos, but not with the intent of creating a full human being. This process is often termed therapeutic or research cloning. The goal is to generate patient-specific embryonic stem cells for medical purposes.
In therapeutic cloning, the human embryo is allowed to develop for only a few days until it reaches the blastocyst stage. At this point, stem cells are harvested from the inner cell mass, which are genetically identical to the somatic cell donor. These cells can be directed to develop into specific cell types, such as nerve, muscle, or pancreatic cells, which can be used to study diseases or potentially replace damaged tissue without the risk of immune rejection.
While human cells and early-stage embryos have been cloned for research, reproductive human cloning—the creation of a full, living human being—has not been achieved. Global scientific and regulatory bodies have placed near-universal bans or severe restrictions on reproductive cloning due to ethical and safety concerns. The current focus of human cloning research remains strictly on advancing regenerative medicine.