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1. The Biology of Stem Cells
2. Introduction to Stem Cell Bioethics
3. Cellular Differentiation
4. Somatic Cell Nuclear Transfer
5. Induced Pluripotent Cells
6. Human Hematopoietic System
7. Human-Animal Chimeras
8. Applications of Stem Cell Science
Current Issues (RSS)
Course Bibliography and Resources
1. Legal History of Stem Cell Science
2. Animal Rights and Welfare
3. Historical Overview of Vertebrate Cloning
4. Ethical Considerations of Egg Donation
5. The Hwang Cloning Scandal
6. Research Ethics and Clinical Trials
7. The Commercialization of Stem Cells
Pages and Files
Historical Overview of Vertebrate Cloning
Table of Contents
Origin of the Term "Clone"
Groundbreaking Cloning Experiments of Hans Spemann
Later CLoning Experiments
Dolly: the First Mammal Cloned from Another Adult Animal
Transgenic Clones and Pharming
Cloning Animals for Food
Cloning and Animal Welfare
The history of vertebrate cloning spans over 100 years (
H.J. Webber (1865 - 1946)
Herbert John Webber was an American botanist from Cornell University who specialized in breeding plants and studying citrus diseases (Knowledge 2011).
Origin of the term “clone”
The word "clone" was coined by H. J. Webber in 1903 to describe a colony of organisms derived asexually from a single
. Seeking a word to describe small sections of a plant that can be cut off and transplanted, Webber chose the word “clon” or clone as a unique new word in the English language, with an easy pronunciation. The word clone derives from the ancient Greek “klon”, or twig, which can give rise to a new tree identical to its parent tree.
Groundbreaking cloning experiments of Hans Spemann
In 1902, Hans Spemann used a strand of baby hair as a noose to successfully split apart the cells of a two-celled salamander embryo, and observed that a normal salamander developed from each individual cell. This was the first recorded instance when scientists could mimic the natural "cloning" that generates monozygotic (identical) twins and triplets.
The next milestone in vertebrate cloning technology occurred 25 years later in 1928. Hans Spemann, still working in the field, transferred a nucleus obtained from a cell isolated from a sixteen-cell salamander embryo to another single salamander embryo cell whose nucleus had been removed
. The enucleated embryo cells fused with the transferred nucleus and developed into a normal salamander. Based on his research, Spemann proposed what he called “the fantastic experiment" that involved cloning by nuclear transfer of adult somatic cells. Unfortunately, he was never able to successfully demonstrate nuclear transfer using adult salamander cells. Hans Spemann was awarded the Nobel Prize in Physiology or Medicine in 1935, for his discovery of the effect now known as embryonic induction (see below).
Hans Spemann and Hilde Mangold
Hans Spemann (1869 - 1941)
, a German embryologist, was often referred to as the father of cloning. In 1928, Spemann was the first to carry out SCNT on amphibian (salamander) embryos and was awarded the Nobel Prize in Physiology or Medicine in 1935 for his discovery of the embryonic induction effect. This effect delineates the path an embryo takes to develop into particular tissues and organs. Spemann’s major collaborator in all of his experiments was Hilde Proescholdt Mangold, his doctoral student.
Hilde Mangold (1898-1924)
was a German biologist working under Hans Spemann. She assisted him in the discovery of embryonic induction. Tragically, Mangold was killed in a domestic accident at the age of 25, just as the paper on embryonic induction was being published (BookRags 2006).
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Later cloning experiments
In the late 1950s, Robert Briggs and Thomas King used the term clone to describe their efforts to produce clones in the frog species Rana pipiens that were genetically identical to a parent frog (
). They used the phrase “nuclear clones” to describe their experiments of transplanting the nucleus from one frog cell to another enucleated cell.
Robert W. Briggs (1911 - 1983) and Thomas J. King (1921 - 2000)
Northern leopard frogs were the first cloned animals. In 1952, two American developmental biologists, Robert Briggs and Thomas King, used somatic cell nuclear transfer (SCNT), with leopard frogs using the same technique that decades later would clone Dolly the Sheep. Their main conclusion was that cells obtained from a newborn have more viability to differentiate and develop as a clone, whereas the cells obtained from the adult animal showed developmental abnormality (Sheperd 2011).
It wasn’t until the 1960s and 70s, however, that a key advance was made by John Gurdon. Gurdon successfully transplanted the nucleus of frog embryos into enucleated oocytes and stimulated these cells to grow to adulthood.
Meanwhile, society was gradually coming to realize that cloning, particularly of human beings, once pure science fiction, might actually be just around the corner. The growing public discussion was one of many expressing concern over the profound implications of these rapid advances in biological science and technology.
In the 1970s, the ethical and social impact of cloning was greatly influenced by an popular book written by Alvin Toffler called Future Shock (1970). In his book, Toffler predicted "...man will be able to make biological carbon copies of himself." Clones, formerly viewed as the simple progeny of asexual reproduction, were now seen as sophisticated products of biological engineering, capable of being used by scientists to control nature for their own agendas. Also, in 1978, a book and later a movie, a thriller by Ira Levin entitled The Boys from Brazil, evoked unsettling images of what living clones might be like, and hinted at the problems and questions that might arise (see also
Module 4 – SCNT
for further discussion).
Fifteen years after Sir John Gurdon’s work, Steen Willadsen and Neal First used nuclear transfer to clone sheep and cows from embryonic cells (see
Di Berardino, McKinnell et al., 2003
for a review).
Sir John Bertrand Gurdon (1933 - )
In 1962, pioneering British developmental biologist Sir John Gurdon of Oxford University cloned the first South African frogs from the nucleus of a fully grown frog intestinal cell. His conclusion, in opposition to that of Briggs and King, was that the genetic information of the cell does not deteriorate as the cell becomes specialized and can be reprogrammed to an undifferentiated state (Oracle 1998).
In 1963, British biologist J. B. S. Haldane, in describing Gurdon’s results, became one of the first to use the word clone in reference to animals.
Alvin Toffler (1928 - )
, an American author as well as business consultant, invented the role of the futurist with his publication known as Future Shock. His writings discuss the world transitioning from first wave (agrarian revolution), to second wave (industrial revolution), to third wave (post-industrial) social orders, and their relevant implications. He forecast a rocketing rate of social and technological changes that will bring about “shattering stress and disorientation,” i.e., Future Shock. His popular maxims are “information overload,” and “change is non-linear and can go backwards, forwards, and sideways” (Toffler, 1970).
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Dolly, the first mammal cloned from a cell from another adult animal (1997)
In 1997, Drs. Ian Wilmut, Keith Campbell, A.E. Schnieke, and other scientists from the Roslin Institute in Scotland used nuclear transfer to generate Dolly, the first mammal cloned from a cell obtained from another adult animal (
Wilmut, Schnieke et al. 1997
). This was a landmark paper and since then, many animals of different species, including dogs, cats, mice, horses, and cows have been cloned using somatic cell nuclear transfer (SCNT) technology.
Steen Willadsen (1944 - ) and Neal L. First (1930 - )
Steen Malte Willadsen
is a Danish reproductive physiologist and alumnus of the Royal Veterinary College of Copenhagen, Denmark. In 1984, as an employee of the British Agricultural Research Council’s Unit, his research led to the first cloned sheep using an embryo donor cell via SCNT (recall that Dolly was cloned using an adult donor cell) (Oracle 1998).
Neal L. First (1930- )
is an American biologist, a professor of Reproductive Biology and Animal Biotechnology at the University of Wisconsin at Madison. His research since the early 1980s focused on the study of sperm and oocyte maturation, embryo production in vitro, cloning of cattle, and techniques to produce transgenic embryos (The-Science-and-Ethics 2001).
Ian Wilmut (1944 - ) and AE Schnieke
Sir Ian Wilmut
is a Scottish embryologist. His work on the cloning of Dolly resulted in contentious bioethical controversies and public debates. In 1974, he joined the Animal Breeding Research Station at Edinburgh, currently known as the Roslin Institute (Academy 2010). He is currently Director of the Medical Research Council Centre for Regenerative Medicine at the University of Edinburgh. In 2008, he was knighted by the Queen of England in honor of his research advances in cloning.
A. E. Schnieke
was the major collaborator of Sir Ian Wilmut in cloning Dolly the sheep (HighBeam 1997).
Transgenic clones and pharming
Producing significant quantities of proteins or other biological substances in their milk or other tissues is another major use of cloning technology in animals. This process is referred to as “pharming” (i.e., pharmaceutical + farming) (
There are two major advantages to cloning large mammals in order to produce proteins in their milk:
it will be economically cheaper than using cell culture technology and,
the milk used to obtain these proteins comes from cloned animals that are free of human infectious agents.
As a case in point, Bio Sidus, an Argentinean company, claimed to breed transgenic cows that could produce enough insulin in their milk to supply insulin for more than 1 million patients with diabetes (
Milk is not the only animal product used in pharming. The yolk of chicken eggs is being studied as another source to produce protein drugs. Chickens have a gestational period of weeks rather than months, and are cheaper to maintain and breed than mammals, making them an ideal alternative to using cows and sheep.
Currently, some other drugs being tested for commercialization using pharming protocols include tissue plasminogen activator (used in treating heart attacks), Factor XIII (used in treating people with hemophilia), and Human Protein C (used as an anticoagulant).
Bioethical concerns raised by pharming
Pharming is the production of human pharmaceuticals – proteins - in the milk of farm animals or in eggs obtained from chickens (Wells 2010). Some proteins can only be produced in large mammals (
Melo, Canavessi et al. 2007
) because the proteins’ chemical structure is so complex that it is not possible to produce them in cell culture or in bacteria. Pharming is the genetic manipulation of cloned animals in the early embryonic stage, so that after birth and once they are grown, they will produce the specific human proteins for which they have been engineered in commercially useful quantities. There are two major advantages to cloning large mammals to produce proteins in their milk:
It is economically cheaper than using cell culture technology;
Use of pharmed animals reduces the risk of transmitting infectious agents to the eventual patients who will be the recipients of the proteins/drugs thus produced; if proteins are obtained from donated human blood plasma, the risk of infection is considerable.
Pharming raises the bioethical objection that these animals are created to be turned into factories. Although they may be treated relatively well, better than factory farmed food animals, so that their biological products are of good quality and uncontaminated, they will not live a reasonably natural life for their species, as was possible under traditional animal husbandry. For obvious reasons, pharmed animals should not be allowed to mingle freely with normal animal populations of any species with which they could interbreed. They should be monitored and controlled so that people cannot use them as a food source.
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Cloning animals for food
The European Union in March/April 2011 debated regulating imports of meat and dairy products from animals bred from clones (
). Crafting the regulations is stalled because the individual states in the EU and the European Parliament cannot agree about the scope of any possible guidelines or laws. European consumer groups mostly are against food from clones. In the United States, Brazil, and other countries, cloning for food is gaining ground, and food manufacturers hope to avoid new and potentially costly labeling requirements.
How do you feel about eating meat from cloned animals? Does the possibility bother you, and if yes, or no, why?
Do you view a cloned animal differently than a naturally bred animal?
Would you view a cloned human being differently than a normally conceived child?
The US Food and Drug Administration (FDA) stated in 2008 that milk and meat from cloned animals and their offspring are as safe to eat as comparable products from conventionally-bred animals. Consequently, the FDA said it would not require food products from cloned animals or their offspring to be labeled as such (
). However, consumer watchdog groups disagree, and find fault with the FDA’s analysis.
Opponents of cloning animals for food production also say the practice raises many animal welfare concerns (for an introductory discussion of animal rights and welfare, see
Supplement 2 - Animal Rights and Welfare
), such as:
extensive suffering of many clones born deformed (e.g., with abnormal digestive tracts, that die early, or that suffer ill health over years);
developmental problems caused by being born with large offspring syndrome (LOS), where the development of some organs outpaces others compared to normal development, and causes maturational, medical and physiological problems;
extensive suffering of many surrogate mother animals that must undergo many procedures, and whose uteri may rupture when giving birth to clones born with LOS;
increased commodification of living animals;
increased efforts to engineer food animals and produce them industrially, at a time when more citizens in the US and other countries - for many reasons - want animal husbandry to curb the abuses of industrial food production and become far more humane;
creating highly uniform animal stocks that could be more vulnerable to diseases that would affect all;
diminishing healthy genetic diversity in populations of farm animals. (see, for example, endanimalcloning.org:
These are the kinds of issues other than food safety that make people uncomfortable with animal cloning. Some surveys indicate that 63 percent of consumers would not buy food from cloned animals even if it were labeled as “safe” (
The Mellman-Group 2006
). Other groups such as Friends of the Earth, an environmental advocacy group based in Washington, DC quote higher figures (see foe.org:
Cloned Food Factsheet
77% of American consumers are “not comfortable” with eating cloned animal products;
81% of American consumers believe that cloned foods should be labeled;
0% of participants in an FDA-sponsored study would feed cloned animal foods to their children.
Concerns about the ethics and morality of cloning, issues the FDA does not consider in its analyses about food safety of clones, as well as concerns for animal welfare, lead the majority of people to oppose cloning animals for food.
Finally, cloning is very expensive, although the advocates’ argument is that the best traits for consumption can be selected and reproduced on a mass scale. Initially one only needs to produce several breeding pairs which could cost, depending on the species, between $12,000 to $30,000 per pair. Greg Jaffe of the Washington, D.C.-based Center for Science in the Public Interest responding to this high cost stated that, "The clones are going to be a minuscule portion of the food supply. What's going to be on people's dinner plates is their offspring." (
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Cloning and animal welfare
Somatic Cell Nuclear Transfer (SCNT): Cloning animals using Somatic Cell Nuclear Transfer (SCNT), as has been pointed out previously in
, is an inefficient and expensive technique to create progeny genetically identical to a parent, by inserting parental DNA into a donated oocyte, to be gestated in a surrogate mother (see
). It is worth remembering that a clone will never be totally identical to its DNA-donor. Epigenetic changes in expression of genes in early development - very influenced by environment - and by any other
and congenital influences on the developing fetus.
Cloning to create a large mammal was first successfully performed by the team led by Sir Ian Wilmut in 1996, creating Dolly the sheep. The reasons for cloning could range from answering basic science questions, to reproducing a beloved, deceased pet, or creating a clone of a high-performing sport or working animal.Some might take issue with private individuals’ motivations to clone special pets, at great expense. Many animal advocates would point out that these are misspent resources, particularly when many appealing animals languish in shelters and are killed if a home is not found within a short time. Even if cloning your loved pet can be done legally, is this manifestation of extreme psychological attachment to one animal desirable and healthy?
According to surveys the majority of Americans do not want to eat the meat of cloned animals, and particularly will not feed this meat to their children, despite federal assurances (
) that it is safe and not different from meat obtained from normally bred animals. This fear may or may not be irrational (
). Perhaps in the future people will accept meat from cloned animals. Many scientific advances once seen as unacceptable, and many foods once deemed too foreign or unpalatable, later were accepted. The unease expressed about eating meat of cloned animals possibly also reflects the sense that these animals are not fully “natural,” leading to a reluctance to be consuming the end product of their unnatural creation. Fears about food safety may not be entirely unfounded. For example, consumer watchdog groups disagree with the FDA’s analysis. Sir Ian Wilmut, the lead scientist who created Dolly, has warned that even small imbalances in a clone's hormone, protein, or fat levels (for example caused by DNA methylation during development) could compromise the nutritiousness, bioavailability of nutrients, or safety of its milk or meat (
From the scientific and medical point of view, the more significant animal welfare concerns are the ones raised by abnormal development - that cloned animals often display abnormal growth patterns and can have serious medical problems from birth on. These were presented above.
The history of cloning reveals many notable scientific achievements and astonishing advances. Discoveries emerging from cloning technologies - stem cells, pharming, and others - continue to yield very important scientific and practical results, with many implications. Cloning has also raised many questions throughout its now considerable history.
Bioethical issues concerning animal welfare have become increasingly important to address with respect to biomedical research and applications of cloning. Today, all principal investigators in both academia and industry must justify:
why they require the use of animals for their experiments
how many animals they plan on using in any given year
that there are no
models to conduct their experiments
the choice of which animal model is to be used in the laboratory becomes increasingly important to ethical research design.
Cloning-related research may move increasingly into
and computational models, but animals of many species will continue to be used in many experiments and particularly in applications.
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Academy. (2010). "Sir Ian Wilmut." Academy or Achievement: A Museum of Living History Retrieved June 30, 2011, from
BookRags. (2006). "World of Genetics on Hilde Proescholdt Mangold." Hilde Proescholdt Mangold Biography, from
Briggs, R. a. K., T.J. (1952). "Transplantation of Living Nuclei from Blastula cells into Enucleated Frog' eggs." Proc Natl Acad Sci U S A 38: 455-463.
Di Berardino MA, McKinnell RG, Wolf DP (2003). The golden anniversary of cloning: a celebratory essay. Differentiation. Sep;71(7):398-401.
FDA (2008). "FDA Issues Documents on the Safety of Food from Animal Clones." FDA Press Release 15 January.
HighBeam. (1997). "2 New Clones Carrying Human Genes: Scientists Hope Sheep Will Make Drug for Hemophiliacs." High BeaM Research, from
Kanter, J. (2011). "E.U. Talks fail on food imports from clone offspring." The New York Times March 29.
McKinnell, R. G. (1985). "Cloning: Of frogs, mice and other animals." University of Minnesota Press, Minneapolis, USA.
Melo, E. O., A. M. Canavessi, et al. (2007). "Animal transgenesis: state of the art and applications." J Appl Genet 48(1): 47-61.
NCSL (2008). "Human Cloning Law." National Conference of State Legislatures.
New-Scientist (2001). "Duplicate Dinner " New Scientist May 19.
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Oracle. (1998). "Steen Willadsen " Oracle'Think Quest : Educational Foundation Retrieved June 30, 2011, from
PressZoom (2007). "Cloned cows can produce Insulin in the milk, claimed thier creators." PressZoom: Global News Service and Press Release Distribution <
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Sheperd, L. (2011). "The History of Cloning." eHow.com Retrieved June 30, 2011, from <
Speeman. (1965). "Nobel Lectures, Physiology or Medicine 1922-1941." Elsevier Publishing Company.
The-Mellman-Group (2006). "Public Sentiment About Genetically Modified Food; Survey Results. The Pew Initiative on Food and Biotechnology. ." The Meller Group 16 November.
The-Science-and-Ethics. (2001). "Neal L. First .,PhD." The Science and Ethics of Human Cloning Retrieved June 30, 2011, from
Toffler, A. "Economics cannot be separated from social, political, cultural, and religious factors, as economists tend to do." Leigh Bureau Retrieved June 30, 2011, from
UCDAVIS. (2008). "Animal Cloning." University of Califonia, Davis: Animal Biotechnology, from
Union (2006). "Scientists say cloning animals for food has uncertain benefits, many drawbacks." Union of Concerned Scientists 28 December.
Weise (2008). "Foes decry clone ruling." USA TODAY 16 January.
Wells, D. J. (2010). "Genetically modified animals and pharmacological research." Handb Exp Pharmacol (199): 213-226.
Wilmut, I., A. E. Schnieke, et al. (1997). "Viable offspring derived from fetal and adult mammalian cells." Nature 385(6619): 810-813.
Human Genome Project Cloning Fact Sheet
Human Cloning Laws set out on the website of the National Conference of State Legislatures,
Table 1 of Lo et al., 2010, Summary of Laws and Guidelines Regarding Human Reproductive Cloning.
Educational website about cloning
, for an engaging do-it-yourself cloning animation
Websites of some companies offering animal cloning technology
Advanced Cell Technology, Inc
, The Cloning Company
For detailed discussion of cloning of food animals from several points of view, see for example:
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