Part 1 of two parts
a.k.a. cell nuclear replacement
Adult DNA cloning topics covered here:
Cloning is the production of one or more individual plants or animals that are
genetically identical to another plant or animal.
Adult DNA cloning involves removing the DNA from an embryo and
replacing it with the DNA from an adult animal. Then, the embryo is
allowed to develop into a new animal with the same DNA as the donor.
It has been used to clone a sheep and other animals. It has not been tried on humans.
With the exception of the sperm and egg, every cell in the body contains all of the
genetic material in its DNA to theoretically create an exact clone of the original body.
But cells have been "biochemically programmed to perform limited functions." 1 The other functions are turned off. Most scientists had
believed that such differentiated cells could not be reprogrammed to be capable of
behaving as a fertilized egg.
In the case of the sheep "Dolly" (described below), a cell was taken from
the mammary tissue of a mature 6 year old sheep while its DNA was in a dormant state. It was
fused with a sheep ovum which had had its nucleus removed. The "fertilized" cell
was then stimulated with an electric pulse. Out of 277 attempts at cell fusion, only 29
began to divide. These were all implanted in ewes. Thirteen became pregnant but only one lamb,
Dolly, was born.
Similar experiments to clone mice were initially unsuccessful. One speculation
was that the
DNA in sheep may not be used by the cells until after three or four cell divisions have
completed. This would give the ovum "sufficient time to reprogram the DNA from
[its original] mammary cell functions to egg cell functions." 1 Both human and mouse use the DNA after the second cell division. So, some researchers had
predicted that humans as well as mice may not be "clonable". However,
mice were successfully cloned later. Thus, cloning of humans might also be
Scientists wondered whether "Dolly" would be fertile. Some cloned frogs are
infertile. Also, cells seem to have an internal clock that causes them to die off after a
normal life. Since Dolly was conceived from a 6 year old cell, her life expectancy may be
reduced from about 11 to only 5 years. This did not take place. Dolly, currently
4.5 years of age, continues to live a normal life.
This was assumed to be impossible in all mammals, until it was achieved in 1996-JUL by a
scientist from the UK, Dr. Ian Wilmut of the Roslin Institute in Roslin, Scotland.
News of the experiment was communicated to the press on 1997-FEB-23. "Dolly," a
seven-month old sheep, was displayed to the media; she is the first large cloned animal
using DNA from another adult. Since Dolly's conception, the Institute has successfully
cloned seven sheep of three breeds. The technique that they developed can probably be applied
to other domesticated mammals, perhaps including humans.
On 1997-MAR-4, apparently in reaction to "Dolly", President Clinton ordered a
widespread ban on the federal funding of human cloning in the US. Research continues in
On 1998-JUL-22, Dr. Ryuzo Yanagimachi of the University of Hawaii announced the cloning of
mice. The team had produced 22 mice; seven of them are clones of clones from the cells of a
Japanese researchers from Kinki University in Nara, Japan cloned 8 calves from a single
adult cow's DNA. They used techniques similar to that which produced "Dolly."
Four died shortly after birth due to what the researchers called "environmental
factors." Their study was published in the issue of Science magazine published
On 1998-DEC-14, researchers at the Infertility Clinic at Kyeonghee University in Korea
announced that they had successfully cloned a human. 2 Scientists
Kim Seung-bo and Lee Bo-yeon took an ovum from a woman, removed its DNA and inserted a
somatic cell from the same 30 year old woman. Their report states: "We were able
to confirm division up to the fourth cell stage, the stage of embryo development when a
test tube embryo is usually placed back in the uterus, where it then further develops into
a fetus." The goal of their research was not to clone humans, but to clone
specific, genetically identical organs for human transplant. They did not implant the
morula into a human uterus because of ethical considerations. They destroyed it. The Korean Federation for the Environmental Movement (KFEM) immediately issued a
statement criticizing the study. Members of the Life Safety Ethics Association held a protest demonstration in front of the university.
Public opinion is having a chilling effect on cloning research in North America. Dr.
Alan DeCherney of the University of California at Los Angeles said that if anyone
tried to clone humans, they would "become the Dr. Kevorkian of reproduction."
By the end of the year 2000, eight species of mammals have been cloned,
including mice, cows, rhesus monkeys, sheep, goats, pigs, and rats. Between 3,000 and 5,000
cloned animals have been produced to date. 3
Current speculation is that the cloning process seems to create random
errors in the expression of individual genes. The egg must have its genes
reprogrammed in minutes or hours during the cloning process. Ova normally
take years to ripen naturally in the ovaries. It appears that the
extremely fast rate of programming can produce random errors in the
clone's DNA. 4
One of many concerns with human cloning is that cloning of animals
sometimes cause fetal overgrowth (aka large-offspring syndrome.) The
fetus grows unusually large and generally dies just before or after birth.
They have under-developed lungs and reduced immunity to infection. Duke
University researchers announced on 2001-AUG-15 that this particular
problem would not exist in humans. The DNA of all primates, such as
humans, monkeys and apes, have two copies of a gene that regulates fetal
growth, whereas almost all other animals have only one. This spare copy
should prevent fetal overgrowth in cloned human fetuses. Randy Jirtle,
professor of radiation oncology at Duke University in Durham, NC, said: "It's
going to be probably easier to clone us than it would be to clone these
other animals because you don't have this problem -- not easy, but easier.'' 5 Kevin Eggan, of MIT's Whitehead Institute works
with cloned mice. He called the Duke study "interesting from the
perspective of the evolution of imprinting genes." But he cautioned
that there is no proof that abnormally large babies are born as a result
of this one genetic difference. His lab has a "four-times normal size"
mouse clone, which has normal IGFR2R genes. He suggests that there are
other factors that can contribute to abnormal development in clones. 6
The following information sources were used to prepare and update the above essay. The hyperlinks are not necessarily still active today.
- Dr. Ray Bohlin, director of communications at Probe Ministries has written an
essay: "The Little Lamb That Made a Monkey of Us All - Can Humans be Cloned Like
Sheep?", 1997-MAR-7. See: http://www.probe.org/docs/lambclon.htm
- "Human Cloning Test Succeeds," Chosun-Ilbo newspaper,
- "Humans may be cloned 'Sooner than anyone thinks.' "
CNSNews.com at: http://www.mcjonline.com/news/01a/20010213e.shtml
- Gina Kolata, "Few cloning efforts work, scientists say,"
New York Times, 2001-MAR-25.
- Will Dunham, "Scientists tout feasibility of human cloning,"
Reuters, at: http://dailynews.yahoo.com/h/nm/
- "Human cloning easier than thought?," CNN, at: http://www.cnn.com/2001/HEALTH/08/14/
Copyright ©1997 to 2016 incl. by Ontario Consultants on
Originally published: 1997-AUG-5
Last updated 2016-MAR-27
Author: Bruce A Robinson