Cloning

The process of making a clone, a genetically identical copy. Cloning can refer to the technique of producing a genetically identical copy of an organism by replacing the nucleus of an unfertilized ovum with the nucleus of a body cell from the organism. The first adult mammal cloned was Dolly the Sheep in 1997.

* * *

1. Growing a colony of genetically identical cells or organisms in vitro. 2. Transplantation of a nucleus from a somatic cell to an ovum, which then develops into an embryo; many identical embryos can thus be generated by asexual reproduction. 3. With blastocysts, dividing a cluster of cells through microsurgery and transferring one-half of the cells to a zona pellucida that has been emptied of its contents. The resulting embryos, genetically identical, may be implanted in an animal for gestation. 4. A recombinant DNA technique used to produce millions of copies of a DNA fragment. The fragment is spliced into a c. vehicle ( i.e., plasmid, bacteriophage, or animal virus). The c. vehicle penetrates a bacterial cell or yeast (the host), which is then grown in vitro or in an animal host. In some cases, as in the production of genetically engineered drugs, the inserted DNA becomes activated and alters the chemical functioning of the host cell.The successful c. of an apparently normal and fertile sheep has shown the possibilities of the technique, but announcement of a proposal to clone a human being has generated controversy and threats of legal prohibition. Opponents of human c. object to the experimental creation of human embryos that would never have the opportunity for implantation and whose eventual destruction would be tantamount to abortion. Many bioethics authorities object even to implantation of an artificially created human embryo into a human uterus. Supporters of c. research fear that legal prohibition will impede needed investigations into human reproduction and infertility. In 1997 the National Bioethics Advisory Commission, after considering the scientific and ethical dimensions of c., recommended a 5-year ban on all human c. research. Nineteen European nations have signed an agreement prohibiting the artificial genetic replication of human beings.

- A/T c. c. of fragments where the only overhanging (or uncomplemented) ends are the A or T bases; occurs often in use of specific enzymes to cut or make DNA fragments.

- positional c. SYN: reverse genetics.

* * *

clon·ing (klōnґing) the formation of a clone.