March 1, Photo courtesy of The Roslin Institute, The University of Edinburgh Cloning is the process of taking genetic information from one living thing and creating identical copies of it.
See Article History Alternative Title: Cloning happens all the time in nature—for example, when a cell replicates itself asexually without any genetic alteration or recombination.
Prokaryotic organisms organisms lacking a cell nucleus such as bacteria create genetically identical duplicates of themselves using binary fission or budding. In eukaryotic organisms organisms possessing a cell nucleus such as humans, all the cells that undergo mitosissuch as skin cells and cells lining the gastrointestinal tractare clones ; the only exceptions are gametes eggs and spermwhich undergo meiosis and genetic recombination.
AP In biomedical research, cloning is broadly defined to mean the duplication of any kind of biological material for scientific study, such as a piece of DNA or an individual cell.
For example, segments of DNA are replicated exponentially by a process known as polymerase chain reactionor PCR, a technique that is used widely in basic biological research. The type of cloning that is the focus of much ethical controversy involves the generation of cloned embryosparticularly those of humans, which are genetically identical to the organisms from which they are derived, and the subsequent use of these embryos for research, therapeutic, or reproductive purposes.
Later, Spemann, who was awarded the Nobel Prize for Physiology or Medicine for his research on embryonic development, theorized about another cloning procedure known as nuclear transfer. This procedure was performed in by American scientists Robert W.
Briggs and Thomas J.
King, who used DNA from embryonic cells of the frog Rana pipiens to generate cloned tadpoles. Gurdon was awarded a share of the Nobel Prize in Physiology or Medicine for this breakthrough.
Advancements in the field of molecular biology led to the development of techniques that allowed scientists to manipulate cells and to detect chemical markers that signal changes within cells.
With the advent of recombinant DNA technology in the s, it became possible for scientists to create transgenic clones—clones with genomes containing pieces of DNA from other organisms.
Beginning in the s mammals such as sheep were cloned from early and partially differentiated embryonic cells. In British developmental biologist Ian Wilmut generated a cloned sheep, named Dollyby means of nuclear transfer involving an enucleated embryo and a differentiated cell nucleus.
This technique, which was later refined and became known as somatic cell nuclear transfer SCNTrepresented an extraordinary advance in the science of cloning, because it resulted in the creation of a genetically identical clone of an already grown sheep.
It also indicated that it was possible for the DNA in differentiated somatic body cells to revert to an undifferentiated embryonic stage, thereby reestablishing pluripotency —the potential of an embryonic cell to grow into any one of the numerous different types of mature body cells that make up a complete organism.
The realization that the DNA of somatic cells could be reprogrammed to a pluripotent state significantly impacted research into therapeutic cloning and the development of stem cell therapies.
Soon after the generation of Dolly, a number of other animals were cloned by SCNT, including pigsgoatsratsmicedogshorsesand mules. Despite those successes, the birth of a viable SCNT primate clone would not come to fruition untiland scientists used other cloning processes in the meantime.
In a team of scientists cloned a rhesus monkey through a process called embryonic cell nuclear transferwhich is similar to SCNT except that it uses DNA from an undifferentiated embryo.
In macaque monkey embryos were cloned by SCNT, but those clones lived only to the blastocyst stage of embryonic development.
It was more than 10 years later, after improvements to SCNT had been made, that scientists announced the live birth of two clones of the crab-eating macaque Macaca fascicularisthe first primate clones using the SCNT process.
The embryo develops into a fetus that is then carried to term. Reproductive cloning experiments were performed for more than 40 years through the process of embryo splitting, in which a single early-stage two-cell embryo is manually divided into two individual cells and then grows as two identical embryos.
Reproductive cloning techniques underwent significant change in the s, following the birth of Dollywho was generated through the process of SCNT. This process entails the removal of the entire nucleus from a somatic body cell of an organism, followed by insertion of the nucleus into an egg cell that has had its own nucleus removed enucleation.
Once the somatic nucleus is inside the egg, the egg is stimulated with a mild electrical current and begins dividing. Thus, a cloned embryo, essentially an embryo of an identical twin of the original organism, is created. The SCNT process has undergone significant refinement since the s, and procedures have been developed to prevent damage to eggs during nuclear extraction and somatic cell nuclear insertion.
Dolly the sheep was cloned using the process of somatic cell nuclear transfer SCNT. While SCNT is used for cloning animals, it can also be used to generate embryonic stem cells. Prior to implantation of the fertilized egg into the uterus of the surrogate mother, the inner cell mass of the egg can be removed, and the cells can be grown in culture to form an embryonic stem cell line generations of cells originating from the same group of parent cells.
Reproductive cloning using SCNT is considered very harmful since the fetuses of embryos cloned through SCNT rarely survive gestation and usually are born with birth defects.
Likewise, attempts to produce a macaque monkey clone in involved cloned embryos, implanted into 50 female macaque monkeys, none of which gave rise to a viable pregnancy.
In Januaryscientists at Stemagen, a stem cell research and development company in California, announced that they had cloned five human embryos by means of SCNT and that the embryos had matured to the stage at which they could have been implanted in a womb.In , the California legislature declared a "five year moratorium on cloning of an entire human being" and requested that "a panel of representatives from the fields of medicine, religion, biotechnology, genetics, law, bioethics and the general public" be established to evaluate the "medical, ethical and social implications" of human cloning (SB ).
Cloning identical primates would decrease the genetic variation of research animals, and therefore the number of animals need in research studies. Similar to previous cloning experiments, Wolf’s team of scientists fused early-stage embryonic cells with enucleated monkey . Cloning’s Historical Timeline B.C.
Mendel comes to be known as the father of genetics. Johann Friedrick Miescher extracts what comes to be known as DNA from the nuclei of white blood cells.
to rush to ban research on the cloning of human beings. It was the successful cloning of various animal species, which laid the foundation of various attempts to clone humans - and thus cannot be ignored when we try to trace the history of human cloning research.
Cloning: Cloning, the process of generating a genetically identical copy of a cell or an organism.
Cloning happens often in nature, as when a cell replicates itself asexually without genetic alteration or recombination. Learn more about cloning experiments, cloning techniques, and the ethics of human reproductive cloning.
Cloning is the process of taking genetic information from one living thing and creating identical copies of it. The copied material is called a clone.
Geneticists have cloned cells, tissues, genes.