In 1995, Dr. Ian Wilmut and Dr. Keith Campbell successfully cloned two mountain sheep, Megan and Morag, from embryonic sheep cells. One year later, in 1996, Wilmut and Campbell successfully cloned the first mammal to be born from an adult somatic cell, specifically an udder cell (a sheep’s mammary gland): Dolly the sheep (Wilmut et al., 1997). In other words, Wilmut and Campbell were able to take a fully differentiated adult cell and revert it back to an undifferentiated, totipotent, state. This was the first time the process had been accomplished for mammalian reproduction. Furthermore, they were able to create a viable pregnancy and produce from it a healthy lamb (however, there were 276 failed attempts before Dolly was created, which, as it will be discussed below, creates concerns over the safety and efficacy of the procedure). Dolly the sheep died in 2003 after having been euthanized due to her suffering from pulmonary adenomatosis, a disease fairly common in sheep that are kept indoors; indeed, many members of Dolly’s flock had succumbed to the same disease. Additionally, she suffered from arthritis. Before she died, she produced six healthy lambs through natural reproduction. Since Dolly, many more mammals have been cloned through the use of SCNT. Some examples are deer, ferrets (Li et al., 2006), mules (Lovgren, 2003), other sheep, goats, cows, mice, pigs, rabbits, a gaur, dogs, and cats. One possible use of reproductive cloning technology is to help save endangered species (Lanza et al., 2000). In 2005, two endangered gray wolves were cloned in Korea (Oh et al., 2008).
65. EGGAN K, AKUTSU H, LORING J, JACKSON-GRUSBY L, KLEMM M, RIDEOUT WM 3rd, YANAGIMACHI R, JAENISCH R. Hybrid vigor, fetal overgrowth, and viability of mice derived by nuclear cloning and tetraploid embryo complementation. Proc Natl Acad Sci U S A 2001 May 22, 98(11):6209-14.
However, what many people find disturbing is the idea of creating agenetic duplicate of an existing person, or a person who hasexisted. That is why the potential application of SCNT in humans setoff a storm of controversy. Another way to produce a genetic duplicatefrom an existing person is by cryopreserving one of two geneticallyidentical embryos created in vitro for several years ordecades before using it to generate a pregnancy. Lastly, reproductivecloning of humans could, in theory, also be achieved by combining theinduced pluripotent stem cell technique with tetraploidcomplementation. Several research teams have succeeded in cloning micethis way (see, for example, Boland et al. 2009). The techniqueinvolves injecting mouse iPS cells in tetraploid embryos, i.e. embryoswith twice the normal number of chromosomes that cannot result in liveoffspring. The resulting mouse pups are derived solely from the iPScells, which means that the tetraploid embryos only acted as asubstitute trophectoderm, which forms the placenta and othernourishing membranes but which does not contribute to the ‘embryoproper’.
Dolly the sheep may have been the world's most famous clone, but she was not the first. Cloning creates a genetically identical copy of an animal or plant. Many animals - including frogs, mice, sheep, and cows - had been cloned before Dolly. Plants are often cloned - when you take a cutting, you are producing a clone. Human identical twins are also clones.
Science/The History of Cloning term paper 12267
Since 1996, when Dolly was born, other sheep have been cloned from adult cells, as have mice, rabbits, horses and donkeys, pigs, goats and cattle. In 2004 a mouse was cloned using a nucleus from an olfactory neuron, showing that the donor nucleus can come from a tissue of the body that does not normally divide.
FREE Genetic engineering and human cloning Essay
This process has been repeated with mice, sheep, monkey's, etc. That is called embryonic cloning. The kind of cloning that created Dolly is when an adult animal is cloned. What happened in Dolly's case is that Ian Willmut and his team of scientists took a nucleus from a Finn Dorset sheep and substituted it with a nucleus of an egg from a Poll Dorset. Once the egg had developed to embryo stage it was implanted into a third breed of sheep a Scottish Blackface. Dolly came out 148 days later as an exact genetic copy of the Finn Dorset.
In 1938, Hans Speman proposed cloning a mammal by transplanting an adult cell’s nucleus into a fertilized egg. This process is called nuclear transfer and was initially used to clone a frog in 1952 (Sinha 59). Using this process, nuclear DNA from the body cell of a donor frog was injected into the egg cell of a recipient frog whose nuclear genetic material was removed. The fused cells divided just like a normal fertilized egg and formed an embryo that was genetically identical to the donor frog. In 1980 mice were successfully cloned using a similar procedure. The nucleus of a body cell of an embryo removed from a pregnant mouse was placed into a fertilized egg of another mouse whose own nucleus was removed. The cell was grown in vitro until it divided and became an embryo. It was then implanted into another mouse and allowed to grow to term. Mammalian clones of sheep were reproduced in this fashion as well in 1984. This type of cloning needed to use embryonic cells. Almost all of an animal’s cells contain the genetic material needed to reproduce that animal. However, as cells differentiate into different tissues and organs, they only keep the genetic material needed to reproduce that organ. Therefore, only embryonic cells can be used for cloning because they have not differentiated into a specific type of tissue and still retain all the genes needed to make a copy of themselves (From Year in Review 1997 1). Although this method of cloning has been successful, most nuclear transfers do not result in live offspring. In addition, there have been a lot of objections raised regarding the use of embryos to clone mammals. Many people object based on religious grounds that the embryo has a soul from the moment of conception and therefore it should not be tampered with. Scientists were hoping that they could clone mammals without the use of embryos (Beddington 3).
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Ever since the announcement of the birth of Dolly three years ago, additional sheep, cows, goats, pigs and mice have been cloned. The desire to produce farm animals with outstanding and useful characteristics is ancient. One of the reasons that cloning is attractive is that it reduces the effort and time needed for farmers to do what they have been doing for years: selecting and propagating the best of the herd. Success with the technique, however, has not been easy in these animals (less than 2% efficiency) and barely achievable in other species such as chickens, monkeys and dogs.
without the genetic “lottery” and mixing that occur in sexual reproduction. It allows an animal with a particular genetic modification, such as the ability to produce a pharmaceutical in milk, to be replicated more rapidly than does natural mating [; ]. Moreover, a genetic modification can be made more easily in cultured cells than in an intact animal, and the modified cell nucleus can be transferred to an enucleated egg to make a clone of the required type. Mammals used in scientific experiments, such as mice, are cloned as part of research aimed at increasing our understanding of fundamental biological mechanisms.Several important concerns remain about the science and safety of nuclear transfer cloning using adult cells as the source of nuclei. To date, five mammalian species -- sheep, cattle, pigs, goats, and mice -- have been used extensively in reproductive cloning studies. Data from these experiments illustrate the problems involved. Typically, very few cloning attempts are successful. Many cloned animals die in utero, even at late stages or soon after birth, and those that survive frequently exhibit severe birth defects. In addition, female animals carrying cloned fetuses may face serious risks, including death from cloning-related complications.