A clone is a genetically identical copy of a living thing. That copy can be as small as a single gene, as ordinary as a plant grown from a cutting, or as complex as an entire animal. The word gets used in science fiction to mean a duplicate person, but in biology, cloning is something that happens naturally every day and has been practiced by gardeners for centuries.
Clones Already Exist in Nature
If you know identical twins, you already know clones. Identical (monozygotic) twins form when a single fertilized egg splits early in development, producing two individuals with the same DNA. This is natural reproductive cloning, and it happens in humans without any technology involved.
Many organisms reproduce entirely through cloning. Bacteria divide by splitting in half, producing two genetically identical cells. Strawberry plants send out runners that take root and grow into new plants. Starfish can regenerate a whole new body from a severed arm. In each case, the offspring carries the same genetic blueprint as the parent. Asexual reproduction like this is one of the most common strategies in the living world.
Three Types of Artificial Cloning
When scientists talk about cloning in a lab, they usually mean one of three things, each with a very different goal.
- Gene cloning produces copies of a specific gene or segment of DNA. This is the most routine form and is used constantly in medical research, such as making bacteria produce human insulin.
- Reproductive cloning produces a whole living animal that is genetically identical to a donor. Dolly the sheep, born in 1996, was the landmark example.
- Therapeutic cloning creates an early-stage embryo not to produce a baby, but to harvest stem cells that match a patient’s DNA. Those stem cells could one day be used to grow replacement tissues for people with injuries or disease. The embryo is never implanted into a womb and does not develop beyond a tiny cluster of cells in a lab dish.
Reproductive and therapeutic cloning share most of the same lab techniques. The difference is what happens after the embryo forms: one path leads to a pregnancy, the other to stem cell research.
How Animal Cloning Works
The technique behind both reproductive and therapeutic cloning is called somatic cell nuclear transfer, or SCNT. “Somatic cell” just means any cell from the body that isn’t a sperm or egg cell, like a skin cell or a mammary cell.
The process works in a series of steps. Scientists first collect a cell from the animal they want to copy. Separately, they take an egg cell from a donor animal and remove its nucleus, which contains the egg’s own DNA. They then insert the DNA from the body cell into the now-empty egg. An electrical pulse fuses the two together, essentially tricking the egg into thinking it has been fertilized. The egg begins dividing and forms an early embryo. For reproductive cloning, that embryo is implanted into the uterus of a surrogate mother, who carries it to term and gives birth to a genetic copy of the original animal.
This is exactly how Dolly the sheep was created. Born on July 5, 1996, Dolly was the first mammal ever cloned from an adult cell. Scientists at the Roslin Institute in Scotland used a cell from a mammary gland, transferred its DNA into an empty egg cell, and implanted the resulting embryo into a surrogate ewe. Dolly’s birth proved something fundamental: that a fully specialized adult cell still contains all the genetic instructions needed to build an entire organism from scratch.
Cloning Is Common in Plants
Gardeners have been cloning plants for thousands of years without calling it that. The major methods are cuttings, layering, division, and grafting. Taking a cutting means snipping a piece of stem or leaf from a parent plant and encouraging it to grow roots, producing a whole new plant with the same DNA. Layering works similarly but keeps the new growth attached to the parent until it roots. Grafting joins a branch from one variety onto the rootstock of another, which is how most fruit trees and grapevines are produced commercially.
Modern agriculture relies heavily on plant cloning. Every Honeycrisp apple you eat comes from a tree that was grafted, not grown from seed, because seeds shuffle genes and produce unpredictable results. Bananas, potatoes, and many ornamental flowers are all propagated as clones to keep their traits consistent.
Clones Are Not Exact Copies
One of the biggest misconceptions about cloning is that a clone will look and act exactly like the original. It won’t, for several reasons.
Even appearance can differ. Many cloned animals have slight variations in coat color and markings. This happens because of how genes are expressed: the DNA may be identical, but which genes get turned on or off during development is influenced by chemical tags on the DNA and by conditions in the womb. Two animals with the same genetic code can end up looking noticeably different.
Behavior is even less predictable. Temperament is only partly genetic. The rest comes from life experience. The FDA uses a helpful example: say you clone your horse because he’s calm and gentle. Your horse learned not to fear loud noises through years of safe exposure. But if the cloned horse has a bad experience during a thunderstorm, like a branch falling on him, he may develop a fear of loud noises that the original never had. Same DNA, different life, different personality. This is the classic nature-versus-nurture distinction, and it applies fully to clones.
Why Cloning Is Still Difficult
Despite decades of progress since Dolly, animal cloning remains remarkably inefficient. In mice, only about 1 to 2 percent of nuclear transfer attempts produce a living animal. Cows have the best rates at 5 to 20 percent. Other species fall somewhere between 1 and 5 percent. For comparison, standard in vitro fertilization in mice succeeds about 50 percent of the time.
The core problem is reprogramming. When you take DNA from a specialized adult cell, like a skin cell, that DNA has been chemically marked to tell it “you are a skin cell.” Those chemical tags need to be erased so the DNA can start over and direct the development of an entirely new organism. Most of the time, the erasure is incomplete, and the embryo fails. Researchers at Harvard Medical School found they could boost mouse cloning efficiency from 1-2 percent up to 8-9 percent by specifically removing those chemical tags, but even that improved rate is far below natural reproduction.
Human Cloning Is Banned Nearly Everywhere
Roughly 46 countries have formally banned human reproductive cloning, including the United States (at the state level in many cases), the United Kingdom, Canada, Australia, France, Germany, Japan, South Korea, Brazil, and India, among many others. In 1998, the Council of Europe issued a protocol explicitly prohibiting “any intervention seeking to create a human being genetically identical to another human being, whether living or dead.”
No verified human clone has ever been born. The combination of legal restrictions, ethical opposition, and the sheer technical difficulty of primate cloning has kept human reproductive cloning firmly in the realm of science fiction. Therapeutic cloning for stem cell research occupies a grayer legal area, with some countries allowing it under strict regulation and others banning it alongside reproductive cloning.