chapter_4_cloning_science_for_class - Chapter 4 Chapter 4...

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Chapter 4 Chapter 4: The science of nuclear transfer technology. Introduction and history Cloning can be defined in broad terms as the identical reproduction of fragments of DNA, genes, cells, or whole organisms from a single ancestor. All cells that divide via mitosis engage in a form of cellular cloning. While most plants and animals reproduce via sexual reproduction, some plants and lower animals engage in asexual reproduction, also a form of cloning. In addition, invertebrates, such as earthworms and starfish, can be cloned or regenerate into two complete organisms if cut into two pieces. This unusual property of complete regeneration disappears as one climbs the phylogenetic scale, but some higher vertebrates such as some lizards sometimes can regenerate a severed tail or limb. The history of vertebrate cloning spans over 100 years (McKinnell 1985). In 1902, Hans Spemann used a strand of hair as a noose to successfully split apart the cells of a two-celled salamander embryo and observed that a normal salamander developed from each individual cell. This was the first recorded instance where scientists could mimic the natural "cloning" that generates identical twins and triplets. Interestingly, the word "clone" was coined by H. J. Webber (Webber 1903) a year later to describe a colony of organisms derived asexually from a single progenitor. The term clone stems from the ancient Greek “klon” which is a twig and probably refers to the fact that a twig can give rise to another tree identical to its parent tree. Looking for a word to describe small sections of a plant that can be cut off and transplanted, Webber chose the word “clon” for its uniqueness and easy pronunciation. 1
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Chapter 4 The next milestone in vertebrate cloning technology occurred 25 years later when Spemann transferred a nucleus obtained from a cell isolated from a sixteen-cell salamander embryo to another single salamander embryo cell whose nucleus was removed. The enucleated embryo cell fused with the transferred nucleus and developed into a normal salamander. Based on his research, Spemann proposed, what he called, “the fantastic experiment," that involved cloning by nuclear transfer of adult somatic cells. Unfortunately, he was never able to successfully demonstrate nuclear transfer using adult salamander cells. In the late 1950s, Robert Briggs and Thomas King (Briggs 1952) used the term clone to describe their efforts to produce frogs that were genetically identical to a parent frog. They used the phrase “nuclear clones” to describe their experiments of transplanting the nucleus from one frog cell to another enucleated cell. However, it wasn’t until the 1960s and 70s that John Gurdon (Gurdon 1962) successfully transplanted the nucleus of frog embryos into enucleated oocytes and stimulated these cells to grow to adulthood. Fifteen years later, Steen Willadsen and Neal First used nuclear transfer to clone sheep and cows from embryonic cells [see (Di Berardino, McKinnell et al. 2003)
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chapter_4_cloning_science_for_class - Chapter 4 Chapter 4...

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