|Why Clone||Process of Cloning||Timeline|
Cloning animals is a reliable way of maintaining high quality livestock to supply our nutritional needs. Identifying and reproducing superior livestock genetics ensures that herds are maintained at the highest quality possible.
Animal cloning offers great benefits to consumers, farmers, and endangered species:
- Cloning allows farmers and ranchers to accelerate the reproduction of their most productive livestock in order to better produce safe and healthy food.
- Cloning reproduces the healthiest animals, thus minimizing the use of antibiotics, growth hormones and other chemicals.
- Cloning can be used to protect endangered species. For example, in China, panda cells are being kept on reserve should this species' numbers be threatened by extinction.
The most common cloning method, known as "somatic cell nuclear transfer" or simply "nuclear transfer," requires two kinds of cell. One is a somatic cell, which is collected from the animal that is to be cloned (known as the "genetic donor"). A somatic cell is any cell other than a sperm cell or egg cell, and contains the complete DNA, or genetic blueprint, of the animal it came from. For cloning purposes, somatic cells are typically obtained by a routine skin biopsy performed by a veterinarian.
The other kind of cell required for cloning is an egg cell, which is collected from a female of the same species (known as the "egg donor"). In the lab, a scientist extracts and discards the nucleus of the egg cell, which is the part of the cell that contains the egg donor's genes. The scientist then inserts the somatic cell from the genetic donor into the egg and "fuses" the two with electricity. The resulting fused egg contains the genetic donor's DNA.
The scientist stimulates the fused egg, which "activates" the egg and causes it to divide just as an egg would if it had been fertilized by a sperm cell in conventional reproduction. The activated egg is then placed in a culture medium. As cellular division continues over the course of several days, a blastocyst (early-stage embryo) forms. After about a week, an embryo transfer specialist transfers the blastocyst to a recipient female (sometimes referred to as "surrogate mother") where it continues to develop. After a full-term pregnancy, the recipient gives birth to an animal that is essentially the identical twin of the genetic donor.
• For an animated walk through the cloning process, click here.
Want to know more about the history of animal cloning? Here is a timeline of milestones in the science and production of cloned livestock.
Arab chieftains first use artificial insemination to produce superior horses.
Hooke discovers the existence of the cell.
Leeuwenhoek sees spermatozoa through a microscope.
Spallanzani discovers that a dog could be impregnated with the cellular portion of semen and that spermatozoa could be inactivated by cooling and then reactivated later.
Mendel, in his study of peas, discovers that traits are transmitted from parents to progeny by discrete, independent units, later called genes. His observations lay the groundwork for the field of genetics.
Miescher discovers DNA in the sperm of trout.
Walter Heap performs the first successful Embryo Transfer in England with rabbits.
Hans Dreisch creates the first cloned animals by blastomere transfer. He isolates blastomeres from 2- and 4-cell sea urchin embryos and observes their development into small larvae.
The Russian throne hires Ivanoff to develop Artificial Insemination (AI) for horses.
Hans Spemman uses a hair from his infant son as a knife to separate a 2-celled embryo from a salamander, which grows externally, and later a 16-celled embryo, all of which develop into adult salamanders.
U.S. Department of Agriculture employee Herbert Webber coins the word "clon" (which evolves into "clone") to refer to "any group of cells or organisms produced asexually from a single sexually produced ancestor."
Spemann performs the first nuclear transfer procedure using salamander embryos.
First commercial use of Artificial Insemination by E.J. Perry.
Spemann proposes a "fantastical experiment" to clone adult somatic cells by nuclear transfer, but cannot perform the experiment because he lacks the necessary technology.
DNA is proven to carry genetic information by Avery.
Artificial insemination of livestock using frozen semen (a longtime dream of farmers) is successfully accomplished.
Briggs and King use nuclear transfer of adult donor cells to clone frogs.
Nature publishes James Watson's and Francis Crick's manuscript describing the double helical structure of DNA, which marks the beginning of the modern era of genetics.
First report of cloning by nuclear transfer seen in newts.
M.C. Chang reports the first unequivocal case of a live birth following egg fertilization in the lab, true in vitro fertilization, and subsequent embryo transfer, to the uterus.
In China, embryologist Tong Dizhou clones a fish.
First report of successful freezing of embryos. Mice embryos survive being frozen to minus 196 and 269 degrees Celsius.
Somatic cell nuclear transfer used to produce cloned frogs.
A sheep is cloned by embryo splitting.
First mammal produced by embryonic nuclear transfer.
Creation of sheep "identical twins" by embryo splitting.
First report of embryonic cell nuclear transfer in an agricultural species (sheep).
Embryonic cell nuclear transfer in cattle.
Sheep and cow embryos cloned, thus pointing out that existing reproductive technology would open the way for large scale cloning in livestock.
Repeated cycles (multiple generations) of nuclear transfer procedures used to produce a large number of identical animals.
First report of a mammal cloned from an embryo-derived cell culture. All prior nuclear transfer had used cells from embryos rather than from cell lines established from embryos. This made it possible to easily clone an unlimited number of animals from a single embryo.
The Roslin Institute in Scotland produces a sheep, Dolly, the first mammal cloned from a cell of an adult animal.
Infigen, Inc. produces Gene, the first cloned cow, from a fetal cell.
Genzyme Transgenic Corporation and Tufts University produce Mira, the first goat cloned from an embryonic cell.
University of Hawaii clones three generations of mice from nuclei of adult ovarian cumulus cells.
Noto and Kaga, the first cows cloned from adult cells, are produced by the Ishikawa Prefectural Livestock Research Center.
The University of Teramo in Italy clones the first mouflon, a rare type of sheep, from an adult cell.
Researchers at PPL Therapeutics produce Millie, Christa, Alexis, Carrel, and Dotcom, the first pigs cloned from adult cells.
Noah, a gaur and the first of an endangered species to be cloned, is produced by Advanced Cell Technologies.
CC, the first female cat cloned and the first clone of a domestic animal, is produced by Genetic Savings & Clone.
University of Georgia and Prolinia clone a cow from a kidney cell drawn from a carcass.
National Academies of Science releases Animal Biotechnology: Science Based Concerns (http://www.nap.edu/books/0309084393/html).
FDA issues the draft executive summary of its Assessment of Safety of Animal Cloning. (http://www.fda.gov/bbs/topics/NEWS/2003/NEW00968.html).
Trans Ova Genetics and Advanced Cell Technologies produce the first bantengs (an endangered species) cloned from adult cells.
Ditteaux, the first African wildcat cloned from an adult cell, is produced by the Audubon Center for Research of Endangered Species.
Dewey, the first deer cloned from an adult cell, is produced by ViaGen and Texas A&M shortly before Christmas.
Idaho Gem, the first mule cloned from a mule fetus, is produced by the University of Idaho.
National Academies of Science releases Safety of Genetically Engineered Foods: Approaches to Assessing Unintended Health Effects and concludes that food produced from clones and their offspring are safe for human consumption (http://www.nap.edu/books/0309092094/html).
Tabouli and Baba Ganoush are the first cats cloned using chromatin transfer technology (CT).
ViaGen, Inc. clones three calves from rare Prime Yield Grade 1 and 2 beef carcasses.
Snuppy, the first clone of a dog, is produced at Seoul National University in South Korea.
Audubon Center for Research of Endangered Species naturally breeds unrelated African wildcat clones, which then gave birth to the first offspring of unrelated clones of a wild species.
The U.S. Food and Drug Administration (FDA) issued three documents on the safety of animal cloning -- a draft risk assessment; a proposed risk management plan; and a draft guidance for industry.
- The US FDA and animal cloning: Risk and regulatory approach. October 2006
- A Risk-Based Approach to Evaluate Animal Clones and Their Progeny - DRAFT. 2006-2007.
- US Food and Drug Administration. 2003. Animal Cloning: A Risk Assessment.
The International Embryo Transfer Society hosted a symposium, “Assisted Reproductive Technologies and Food Safety in Farm Animals,” in Kyoto, Japan. Presenters from seven countries presented data in agreement with the FDA’s Draft Risk Assessment.