A clone is a genetic copy: a gene, a cell, or a whole organism that carries the same genetic makeup as the one it came from.1Genome.gov. Cloning Fact Sheet The word covers far more than lab-made sheep. Most clones on Earth were never made by people, since many plants, some animals, and even human identical twins arise this way. Sharing every gene doesn’t make a clone a duplicate, though, because genes are only part of what shapes a living thing.
What Makes Something a Clone
In sexual reproduction, a child gets half its genes from an egg and half from a sperm. A cloned individual would instead receive all of its genes from a single individual.2web.stanford.edu. What Is a Clone: Definition and How It Works Several different processes, natural and technical, can produce such copies.3Genome.gov. Cloning Fact Sheet4Genome.gov. Cloning Fact Sheet
That single source is the test, not the method. A runner that roots, a split embryo and a lab-built embryo all qualify, because each draws its genes from one individual. Ordinary siblings differ from each other because the mixing of two parents’ genes is shuffled each time; identical twins are the exception. A clone skips that shuffling entirely. Small copying errors (mutations) can still arise as cells divide, so a clone matches its source very closely but not necessarily at every single letter of DNA.
The word gets used at three levels. At the molecular level, a clone is a copied stretch of DNA, such as one gene. At the cellular level, it is a group of cells all descended from one cell. At the level of the whole organism, it is a plant or animal that genetically matches another. News stories about cloning usually mean that last kind.
A common misunderstanding is that a clone is an instant adult copy. A cloned animal starts life as an embryo and is born a baby, and it has to grow up over the same years any animal would. Memories, training and personality are not carried in DNA, so they cannot be copied.
How Scientists Clone an Animal
The standard method, called nuclear transfer, means moving the nucleus of an ordinary body cell, such as a skin cell, into an egg.5PubMed Central. A Road Map for 21st Century Genetic Restoration: Gene Pool Enrichment of the Black-Footed Ferret The donor cell is usually taken from a small tissue sample from the animal being copied and grown in a dish, so many cells are available. The egg comes from a different female of the same species, collected at the stage just before it would normally be fertilised.
From there, nuclear transfer has three main steps. First the egg’s own nucleus is removed, which is done under a microscope with fine glass tools. Then the donor nucleus is injected or fused in, sometimes with a brief electric pulse. Finally the rebuilt embryo is chemically activated to start dividing.6PubMed Central. Somatic Cell Nuclear Transfer Reprogramming: Mechanisms and Applications
The early embryo is usually grown for a few days in the lab to see whether it keeps developing. Healthy-looking ones are placed in a surrogate mother, who carries the pregnancy to birth. Pregnancies are monitored closely, because cloned pregnancies can run into problems that ordinary ones do not. The offspring carries the nuclear DNA of the donor, not of the egg or surrogate.7PubMed Central. A Road Map for 21st Century Genetic Restoration: Gene Pool Enrichment of the Black-Footed Ferret
The emptied egg still supplies its cytoplasm and tiny energy-making structures, which have their own DNA. So a clone is not a perfect match for every last bit of DNA, and the surrogate’s womb also shapes the clone before birth. That is why scientists say clones share nuclear DNA specifically.
Dolly the sheep, born in 1996 and announced in 1997, was the first mammal cloned from an adult body cell.8PubMed. The recent history of somatic cloning in mammals Her birth showed that a fully specialised adult cell still holds the instructions to build a whole new animal.
Most attempts fail. Many rebuilt embryos never start developing or stop early, and few of those placed in surrogates result in live births. Each species needs its own adjustments to the method.
Is a Clone an Exact Copy
Identical twins show that genes aren’t the whole story. They come from one fertilised egg, so they are natural human clones sharing almost all their genetic variants.9PubMed Central. Epigenetics of discordant monozygotic twins: implications for disease Yet most identical twins still differ in disease risk and physical features.10PubMed Central. Epigenetic differences arise during the lifetime of monozygotic twins A major reason is chemical tags on DNA that switch genes on or off, and these tags drift apart as twins age.11PubMed Central. Epigenetic differences arise during the lifetime of monozygotic twins Twins who were older, lived apart longer, or had different health histories showed bigger differences.12PubMed Central. Epigenetics of discordant monozygotic twins: implications for disease
These switches act like dimmers, deciding how much of each gene a cell uses without changing the DNA letters. Diet, illness, stress and other life experiences can shift them. Unlike twins, a lab clone is born at a different time and often to a different mother, so it grows up in different years, homes and circumstances, which widens the differences.
Lab clones add a further complication: they carry leftover switches from the donor cell. In most cloned embryos, the donor cell’s gene switches are not fully reset to an embryo’s starting state.13PubMed. Conservation of methylation reprogramming in mammalian development: aberrant reprogramming in cloned embryos This incomplete reset likely explains why cloning so often fails.14PubMed. Conservation of methylation reprogramming in mammalian development: aberrant reprogramming in cloned embryos Many clones that are born develop abnormalities likely caused by faulty resetting.15PubMed. Nuclear cloning and epigenetic reprogramming of the genome
A normal embryo begins with a fresh, blank pattern of switches, while a donor cell arrives with the pattern of a skin cell, for example. The egg has only a short time to rewrite that pattern, and it rarely does so perfectly.
For owners of cloned pets, this means expecting resemblance with clear differences. Coat patterns can differ because markings form partly by chance in the womb. Temperament depends heavily on upbringing and experiences. A cloned pet will not remember its owner or past life.
Clones That Occur in Nature
Plants clone themselves through vegetative growth:
- Bulbs: daffodils store food and grow internal buds into new shoots the next year.16a level biology student. 22.1 Natural Cloning in Plants
- Runners: spider plants send out a side stem that roots when it touches soil.17a level biology student. 22.1 Natural Cloning in Plants
- Rhizomes: marram grass has underground stems that send up new shoots.18a level biology student. 22.1 Natural Cloning in Plants
- Tubers: potatoes are swollen stem tips whose buds become new plants.19a level biology student. 22.1 Natural Cloning in Plants
A new plant from any of these starts with a ready supply of stored food from the parent, giving it a head start over a seedling. Because the offspring is a clone, a plant well suited to a spot can spread across it quickly, forming large patches of identical plants.
If you garden, you already clone plants. Rooting a stem cutting creates a copy of the parent plant, and dividing a clump of perennials does the same. A sprouted potato grows a copy of the original variety, and named fruit varieties are kept true by grafting, which is also a form of cloning.
Some animals clone themselves too. In parthenogenesis, an unfertilised egg develops into offspring genetically identical to the mother.20Gemini Genetics. Cloning In Nature- Learn About Cloning In The Natural World It is known in some insects, reptiles and fish, and in some species it is a regular way of reproducing. Brittle stars, relatives of starfish, can instead split and regrow into new individuals.21Gemini Genetics. Cloning In Nature- Learn About Cloning In The Natural World
Copying Genes in the Lab
In molecular biology, cloning means copying a single piece of DNA, and bacteria do the work. The DNA piece of interest and a small circular carrier DNA are cut with molecular scissors.22SnapGene. The Plasmid Cloning Cycle An enzyme then glues the piece into the carrier, forming DNA combined from two sources.23LibreTexts Biology. What Is a Clone: Definition and How It Works The carrier goes into bacteria such as E. coli, which copy it each time they divide.24PubMed Central. Brief guide to gene cloning25SnapGene. The Plasmid Cloning Cycle One piece of DNA becomes millions of copies.
The scissors are restriction enzymes, proteins from bacteria that cut DNA at particular short sequences. Cutting both the gene and the carrier with the same enzyme leaves matching sticky ends that fit together. The glue is another enzyme, which seals the joined pieces into one continuous strand.
Only a small share of bacteria take up the carrier, so the mix has to be sorted afterwards. Carriers often include a gene for resisting an antibiotic, so growing the bacteria on antibiotic-laced dishes leaves only those holding the carrier. The surviving colonies each grow from a single bacterium, so each one is a clone of that cell.
No animal is created this way, and most cloning in labs today is this molecular kind. Medical insulin is made by bacteria carrying a copied human gene, and many vaccines and diagnostic tests rely on copied genes.
What Animal Cloning Is Used For
Animals are cloned commercially for farming, research, racing camels and horses, and detection dogs.26Wikipedia. Commercial animal cloning On farms, clones mainly serve as breeding stock, not food, so their ordinarily bred offspring become the food animals.27U.S. Food and Drug Administration. A Primer on Cloning and Its Use in Livestock Operations A clone of a top animal is valuable for its genes, which are passed into regular herds through ordinary breeding. Cloning is too expensive to produce animals for meat or milk directly.
Cloning paired with gene editing makes research animals. Scientists edit genes in a body cell, then clone it, producing animals with the change in every cell.28PubMed Central. Generation of CRISPR/Cas9-mediated gene-targeted pigs via somatic cell nuclear transfer This has produced pigs and dogs used to study diseases such as Parkinson’s, without detected unintended edits.29PubMed Central. Generation of genome-edited dogs by somatic cell nuclear transfer30PubMed Central. Generation of CRISPR/Cas9-mediated gene-targeted pigs via somatic cell nuclear transfer Editing a single cell in a dish is far easier than editing a whole embryo, and the cell can be checked for the intended change first. Such animals can model a human disease more closely than mice sometimes do.
Reproductive cloning aims at a new individual, while therapeutic cloning makes embryos only to get stem cells.31Asploro Journal of Biomedical and Clinical Case Reports. Ethical Debates about Cloning Those stem cells could become patient-matched tissue for treatment.32PubMed. Using therapeutic cloning to fight human disease: a conundrum or reality? Reprogrammed skin cells, called induced stem cells, now offer a route without embryos.33PubMed Central. To Clone or Not to Clone? Induced Pluripotent Stem Cells Can Be Generated in Bulk Culture
Clone-heavy crops carry a risk. Cavendish bananas are clones making up over 40% of bananas grown worldwide.34PubMed. The Vulnerability of Bananas to Globally Emerging Disease Threats Because they are genetically alike, one disease can threaten them all.35PubMed. The Vulnerability of Bananas to Globally Emerging Disease Threats
Can Cloning Save Endangered or Extinct Species
Frozen cells can give endangered species a second chance. A black-footed ferret that died in 1988 was cloned from frozen cells, producing three healthy kits.36bioRxiv. First endangered black-footed ferrets, Mustela nigripes, cloned for genetic rescue Her genes, absent from living ferrets, can now widen the species’ tiny gene pool.37bioRxiv. First endangered black-footed ferrets, Mustela nigripes, cloned for genetic rescue Cloning across species is difficult, though, and must be worked out separately for each animal.38PubMed Central. A Road Map for 21st Century Genetic Restoration: Gene Pool Enrichment of the Black-Footed Ferret
The ferret’s genes were saved by chance, because cells had been stored long before cloning was possible. That is why conservation groups now keep frozen collections from rare species.
One clone helps a species only a little at first. She is a single animal, so she must breed with living animals to pass on her added variety. Cloning cannot by itself fix threats such as habitat loss, so it supports other conservation work.
DNA breaks down after death, so cloning long-dead organisms is unlikely to work.39Functional Ecology. Pathways to de‐extinction: how close can we get to resurrection of an extinct species? Species with no preserved living cells may never be resurrected.40PubMed Central. De-Extinction Even with a full genome, a revived animal would differ because environment shapes it.41Functional Ecology. Pathways to de‐extinction: how close can we get to resurrection of an extinct species?
Mammoth headlines describe something else. Those projects edit an elephant’s genes to add mammoth traits, and the result is a look-alike hybrid, not a true mammoth. For most extinct species, gene editing is the only route.42PubMed Central. De-Extinction Even then, the original animal’s behaviour, learned from its herd, is lost.
Do Clones Age Early
Telomeres are protective caps at chromosome ends. Each time a cell divides they shorten slightly, so their length acts as a rough record of how many divisions a cell has been through. They shorten with age, and the fear was that clones made from adult cells would be born old.43PubMed. Cloning adult animals – what is the genetic age of the clones? Telomere length is only one marker of aging, and it does not predict lifespan on its own.
Dolly fuelled that worry. She developed arthritis and lung disease and died at six, while sheep often live about ten to twelve years. But her lung disease was common in indoor-housed sheep, and later studies of cloned sheep found many aged normally.
The telomere results are mixed. Cows cloned from nearly worn-out cells had telomeres longer than newborns’.44PubMed. Extension of cell life-span and telomere length in animals cloned from senescent somatic cells Eggs contain factors that can rebuild telomeres in the new embryo, which fits with the longer telomeres seen in some clones. Yet in cattle, clones from some cell types had shorter telomeres than normal.45PubMed Central. Will cloned animals suffer premature aging – The story at the end of clones’ chromosomes The results vary with the donor cell type and the method, so a clone’s cellular age depends partly on which cell was used.