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Pronunciation: klon'ing


  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. Replication of genetically identical embryos by microsurgical division of a blastocyst and implantation of resulting cells in animal wombs for gestation.
  4. “Therapeutic” cloning: growth of somatic stem cells in an embryo that has been produced by fertilization in vitro and modified by replacement of its nuclear material with DNA from a host with deficient or diseased tissue (heart, liver, pancreas). Subsequent harvesting of the stem cells for implantation in the host subject results in destruction of the embryo.
  5. A recombinant DNA technique used to produce millions of copies of a DNA fragment. The fragment is spliced into a cloning vehicle (plasmid, bacteriophage, or animal virus). The cloning 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.

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© Copyright 2018 Wolters Kluwer. All Rights Reserved. Review date: Sep 19, 2016.