基因工程习题及参考答案

基因工程习题及参考答案内容摘要：

ed anism can grow from the egg cell, as in the case of a fertilized egg. In the case of therapeutic cloning the diploid nucleus es from the patient in whom destroyed tissue is to be replaced, . following a heart attack or a spinal injury. In contrast to reproductive cloning, the embryo that has been created artificially by means of a nucleus transfer is not implanted in the uterus of a prospective mother. Instead, in the socalled blastocyst stage of development (about the sixth day) the inner cells are removed from the embryo, destroying it in the process. The stem cells taken from the embryo are used as a raw material for the development of the cell/tissue types needed. The cells or tissues grown from them will not be rejected later when they are transferred to the patient, since they are geically identical with those already in the patient39。 s body. In contrast to the transplantation of cells and tissues customary today, no medication is needed to suppress defensive reactions of the immune system and the longterm survival of implants bees feasible. Therapeutic and reproductive cloning in humans is prohibited in Germany under the provisions of the Embryo Protection Act. In the United Kingdom of Great Britain and Northern Ireland therapeutic cloning in humans is now possible under strict regulations, but reproductive cloning continues to be prohibited. It is assumed that many years of research are needed yet before cells or tissues can be transferred successfully in humans on the basis of therapeutic cloning. There has not been enough research carried out thus far on the extent to which the growth of transplanted cells and tissues can be controlled and whether tumors or malignant tissue growth could occur. The cloning of plex ans such as hearts or kidneys is currently beyond reach. 10 What are stem cells? Stem cells are the predecessors of more differentiated and, as such, more specialized cells. Bonn marrow, for instance, contains stem cells for the various cells that occur in blood such as lymphocytes, granulocytes, or thrombocytes. Stem cells show different degrees of differentiation. They may have the ability to develop into a plete anism, into a variety of different cells, or into specific cells only. These stages are reflections of embryonic development. In the first days after fertilization embryonic stem cells have what is known as totipotence, . the ability to develop into a plete anism. In the further course of development they have varying degrees of pluripotence, . the ability to develop into specific tissues with specific functions such as liver, kidney, or brain tissue. Small numbers of stem cells are found in these types of tissue in adults or in the blood of the umbilical cords of newborn babies. The latter could possibly serve as an alternative for embryonic stem cells. The extent to which this is the case is currently a subject of research. Members of the medical munity attach considerable hope to stem cell research. They see potential for being able to replace damaged tissues such as myocardial tissue after a heart attack or nerve tissue in the brain in connection with the treatment of Parkinson39。 s disease or in the spinal cord after back injuries. Adult cells cannot be used for this, since they, in contrast to stem cells, are no longer able to integrate themselves into the tissue of an an and take over the necessary functions. It is of fundamental importance for implementation in clinical practice to be able to grow unlimited numbers of stem cells at specific levels of differentiation potential and, at the same time, to be able exert precise control over their growth into certain types of cells as needed. Similar to the situation given in connection with therapeutic cloning, questions as to the ability to control tissue growth and potential for the formation of tumors and malignant tissue are still unanswered. There is a need for extensive research here. 11 What is a transgenic anism? A transgenic anism is an anism, into the geic material of which exogenous genes have been introduced with the help of geic engineering methods. This process is also called geically engineered change, gene manipulation, or germ line modification in reference to animals. Transgenic anisms pass on the new geic information to their offspring. Manipulation of human germ lines is prohibited in Germany. Transgenic animals are being used to a growing extent in medical research, . transgenic mice for research on the CreutzfeldtJakob disease (CJD). Transgenic plants are being developed mostly for use in agriculture. Transgenic microanisms have been used primarily in the production of medicines and enzymes. Other uses of geically modified microanisms include food processing and the production of biodegradable plastics. In some cases transgenic animals, plants, and microanisms have been patented. 12 What does xenotransplantation mean? Xenotransplantation means the transplantation of animal ans, tissues, or cells into humans as well as exposure to animal ans or cells through the bloodstream. Although primates were originally considered to be suitable donors for xenotransplantation, pigs are now considered to be a better choice for a number of reasons. The transplantation of entire ans from pigs is prevented by uncontrollable hyperacute reactions of the human immune system. The blood vessels of the transplanted an clog up within a few minutes and the an dies. An attempt is being made to create donor animals geically engineered to reduce or entirely eliminate the rejection of transplants by the immune system. At present it is not yet possible to say whether xenotransplantation will bee a clinical reality. There are fundamental reservations with regard to xenotransplantation. They derive from the fear that new。