Transgenic Animals Introduction, Genome Manipulations, Niemann Rath, Somatic Gene Therapy, Microinjection, Pronuclei

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	Transgenic Animals Introduction The genetic alteration of animal by man has been the driving force behind the domestication of wild animals. The animal breeding programmes carried out since the last century have become much more consistent in pursuing the selective, purposeful and noticeable alteration of individual traits. The extreme development of certain traits is the result of formulating distinct breeding aims. The improvement of milk yields in dairy cows may serve as an example. While the annual milk yield per cow was approximately 1000 kg in the middle of the 19th century, it reached more than 7000kg in some populations at the end of the 1980s with herd averages of over 10,000kgs. The difficult problem in animal breeding is with the complex genotypes responsible for the development of desired phenotypic traits. Frequently, information about the genetic causes of certain phenotypic characters can be animals (pedigree analysis and estimation of breeding values.) The most important question regarding phylogenetically determined characters is the distinction between genetic and environmental influences for the evaluation of the cause-and-effect relationships between genotypes and phenotypes.
During the last few years, new methods have been developed which, unlike conventional breeding techniques, allow the genetic composition of organisms to be modified directly and selectively rather than indirectly by estimating the breeding values on the basis of phenotypes in order to establish ranking order for selection. In principle, these new techniques of genetic manipulation can be categorized into those which treat the entire genome as a compact unit (genome manipulation; e.g. nuclear transfer) and those in which individual genes are manipulated (gene manipulations; e.g. gene transfer). Further, these techniques can be differentiated into those allowing manipulation of somatic cells (e.g. somatic gene therapy) and those directed at altering the germ line of animals. The latter techniques give rise to transgenic lines of animals characterized by the stable transmission of the genetic modification.
The application of gene transfer techniques has furnished new insights in the developmental biology and the principle underlying tissue-specific gene expression. Gene transfer allows the development of new production system for pharmaceutically important proteins. As far as animal production is concerned, gene transfer appears to be a promising technique for improving disease resistance, performance of the quality of animal products by modifying, for example, metabolic pathways, and hormone status.
Recently, progress has been achieved in reproductive biotechnology in swine with special reference to in vitro production of embryos, generation of identical multiples and transgenic pigs useful for xenotransplanation (Niemann and Rath, 200 1). In vitro production (in vitro maturation, in vitro fertilization and in vitro culture) of viable porcine embryos is possible, although with much lower success rates than in cattle. The main problems are insufficient cytoplasmic maturation of porcine oocytes. The generation of the first piglets from somatic cell nuclear transfer has been achieved. DNA microinjection into pronuclei of porcine zygotes has reliably resulted in the generation of transgenic pigs, which have special importance for the production of valuable pharmaceutical proteins in milk and xenotransplantation. It has been demonstrated that by expression of human complement regulatory proteins in transgenic pigs, the hyper-acute rejection response occurring after xenotransplantation can be overcome in a clinically relevant manner .
	Gene transfer is an experimental process for modifying the heritable genotypic and phenotypic content of the cell by causing the cell to take up and express gene sequences of purified DNA from donor cells. A successful germ -line transmission of incorporated DNA was also observed. These spectacular results captured the imagination of the scientific community and are the basics for a flourishing research and commercial interest in the area of transgenic animal production. There have been two basic strategies employed in these efforts. The first involves the production of the transgenic animals by transmitting into the latter a production trait which enhances the animal's value as a producer of conventiona1 animal product. The second strategy in producing transgenic animals is to generate animals that biosynthesize a commercial product other than the conventional animal product.

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Microinjection Embryo Transfer Use of Embryonic Stem Cells Retroviral Vectors Transmission of Transgenes Nuclear Transfer (NT) Applications of Transgenic Mice Disease Models Applications of Transgenic Mice Oncogenes Applications of Transgenic Livestock Growth and Carcass Composition Biochemical Pathways and Quality of Products Production of Pharamaceuticals and Biomolecules Human Proteins Secreted Milk of Transgenic Livestock Antibody Production in Transgenic Animals Gene Pharming Disease Resistance Transgenic Strategies to Increase Disease Resistance Transgenic Approaches to Increase Disease Resistance of the Mammarygland Environmentally Friendly Farm Animals Xenotransplant Transgenic Animals as a Model For Human Diseases

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