【正文】 auses and diagnosis of hereditary diseases, and the search for possible therapies. Diagnostic procedures today include stateoftheart geic diagnoses in addition to traditional analyses of hereditary mechanisms. 5 What potentials are held out by geic diagnosis? Modern geic diagnosis methods make it possible to analyze individual structures of the genome and, in doing so, to identify gene defects associated with hereditary diseases such as cystic fibrosis. This would be beneficial to persons who carry the gene and would run the risk of passing it on to their children. It is conceivable that awareness of an inherited predisposition for a disease that emerges later in life would cause the persons in question to take special precautions such as going in for preventive checkups or pursuing a lifestyle aimed at preventing an outbreak of the disease. Gene tests can be used to confirm the diagnosis of suspected diseases. More than that, modern methods (such as gene chips) can be used to help a wide range of people, including those who are not sick, to identify geic characteristics such as predispositions for certain diseases. Here, entirely new ethical and legal questions are arising for society. In the case of predictive gene tests, . tests used to make forecasts as to risks of hereditary illness, it will be a separate task to determine whether these tests will be of value to individuals and to society as a whole. We need to distinguish between preimplantation geic diagnosis (PGD), prenatal geic diagnosis in the context of prenatal care, and postnatal geic diagnosis. Preimplantation geic diagnosis (PGD) is a controversial area of geic diagnosis. After in vitro fertilization PGD can be used to carry out a gene test on an embryo before it is implanted in the mother39。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 offspring. The predisposition for a given disease will be passed on to the patient39。除此之外噬菌體和質(zhì)粒還有哪些可能的方式避免宿主的限制系統(tǒng)？ “限制 ”酶？ ？ ？ ？ A 和 .RNase H 在催化活性和應用上有何不同？ DNA 前，用 DNaseⅠ 處理 DNA 時，應注意什么？ DNA的復制是很重要的，但 RNA的合成一般卻不需要連接酶，為什么？ 聚合酶 Ⅲ 特異性地轉錄小分子 RNA，但 為什么不轉錄 ? EcoR Ⅰ 切割外源 DNA 片段時出現(xiàn)了星號活性，可能是什么原因？ 二、參考答案： 1 What are biotechnology and geic engineering? Biotechnology is a field of bioscience. In very general terms it can be described as the theory of the use of biological systems in research and applications. Biotechnology applications are a rapidly growing sector of the economy. The number of biotech panies in Germany has increased considerably over the past seven years. Geic engineering includes all biotechnological processes aimed at effecting specific changes in the geic material of cells. The principle is, in general, the following: sections of DNA (= deoxyribonucleic acid) from outside sources are introduced into a cell in order to bring about defined changes. What is involved in most cases is the synthesis of molecules, the information for which is contained in the introduced DNA. This process has been used to produce new medicines (see geically engineered medicines). 2 What is a gene? A gene is the smallest unit of geic material. It describes a specific section of DNA which, as a result of its nucleotide (= DNA ponent) sequence, determines specific functions, characteristics, features, or structures of a cell. The way genes are expressed in each case is dependent on their interaction with other genes and with the environment. The genome is the entirety of genes contained in an anism. The term is synonymous with geic material. 3