新编英语教程 4 Unit 13 拓展知识.ppt

Further development1.definition of cloningCloning,creatingacopyofliving matter,such as a cell or organism.The copies produced through cloning have identical genetic makeup and are known as clones.Many organisms in nature reproduce by cloning.Scientists use cloning techniques in the laboratory to create copies of cells or organisms with valuable traits.Their work aims to find practical applications for cloning that will produce advances in medicine,biological research,and industry.2.HOW SCIENTISTS CLONE CELLSA.Blastomere Separation Inblastomereseparation,scientists fertilize an egg cell with a sperm cell in a laboratory dish.The resulting embryo is allowed to divide until it forms a mass of about four cells.Scientists remove the outer coating of the embryo and place it in a special solution that causes the individual cells of the embryo,known as blastomeres,to separate.Scientists then put each blastomere in culture,where it forms an embryo containing the same genetic makeup as the original embryo.Each new embryo can then be implanted into the uterus of a surrogate mother to develop during a normal pregnancy.B.Blastocyst DivisionInblastocystdivision,scientists allow a fertilized egg to divide until it forms a mass of about 32 to 150 cells,known as a blastocyst.Scientists then split the blastocyst in two and implant the two halves into the uterus of a surrogate mother.The two halves develop as identical twins.C.Somatic Cell Nuclear TransferWhileblastomereseparation and blastocyst division produce animals containing the genetic material from both a mother and father,somatic cell nuclear transfer produces an animal carrying the genetic material of only one parent.In this technique,scientists transfer the genetic material from a donors somatic cell(any body cell other than an egg or sperm cell)to an enucleated egg cellthat is,an egg cell with its nucleus,and thus its genetic material,removed.The resulting cloned cell contains the genetic material of the donors somatic cell.Genetic EngineeringGenetic engineering enables scientists to produce clones of cells or organisms that contain the same genes.1.Scientists use restriction enzymes to isolate a segment of deoxyribonucleic acid(DNA)that contains a gene of interestfor example,the gene regulating insulin production.2.A plasmid removed from a bacterium and treated with the same restriction enzyme binds with the DNA fragment to form a hybrid plasma.3.The hybrid plasmid is re-inserted back into the bacterium,where it replicates as part of the cells DNA.4.A large number of identical daughter cells(clones)can be cultured and their gene products extracted for human use.First Cloned Cat The worlds first cat clone,named CC,for carbon copy or courtesy copy,was produced by scientists at Texas A&M University in College Station.Born December 22,2001,the kitten was cloned using a method called nuclear transfer,in which nuclei from cells of an adult animal are inserted into egg cells with nuclei removed.The embryos that result are then implanted into the uterus of a surrogate mother,where they develop in a normal pregnancy.Identical Calves Two of eight calves cloned from cells obtained from one adult cow stand in a field in Ishikawa,Japan.The calves were cloned by researchers at Kinki University in Nara,Japan.The results of the cloning experiment were published in 1998.