When the animals are genetically manipulated by introducing a gene, they are said to be transgenic animals or transgenics. The foreign gene which is inserted expresses its character in the animal and inherited for generation. These transformed animals - transgenics produce some valuable therapeutic proteins, more milk & represent fast growth. Some of the animals are -
Transgenic Mice - The foreign gene can be introduced by following method.
a) Retroviral Method - The desired gene is incorporated into a retroviral DNA and then retrovirus with recombinant RNA is made. The produced virus is injected in a 8 celled embryo which is implanted in the uterus of female mouse. The mouse gives transgenic offsprings.
b) Microinjection Method - The foreign gene is injected into male pronucless in the fertilized egg. Then the zygote is implanted in a female mouse.
c) Transfection Method - From a blastocyst, embryonic stem cells are taken and with the help of transfection it is introduced to the cells. The transfected cells are introduced into blastocyst from female and implanted in the female.
Transgenic mice represents human disease models for AIDS, diabetes, cancer and immune functions. They help in studying gene regulation, immunulogical reactions and tumour development. They are used to produced valuable threapeutic value protein in order to treat human diseases, also assess the credibility of medicine to use for human diseases.
Transgenic Cattle - Oocytes from cows are fertilized in vitro by semen of the bull. The fertilized oocytes are centrifuged. The yolk is settled on one pole and foreign gene is microinjected in to the male pronucleus. The resulted oocytes are allowed to grow upto blastocytes stage and then blastocytes are implanted in the uterus of the cows. Transgenic siblings are produced. Transgenic cows are used for producing milk rich in k-caesin (cheese making milk), also milk poor in lactose for lactose intolerant people.
Transgenic Sheep - Mammary glands of genetically engineered sheep produce proteins of therapeutic value example a1-anti trypsin (ATT), factor IX etc. a1-anti trypsin injection cures emphysema (a lung disease in human). ATT gene with beta-lactoglobin is injected into male pronucleus of fertilized egg. The egg is then implanted into the female which produce transgenics. Transgenic sheep with factor IX gene is used to treat haemophilia in man. Factor IX is isolated from the milk and used.
Transgenic sheep having growth hormone gene (keratin gene or cystine gene) produce high quality wool.
Transgenic Pig - Gene for factor VIII is inserted in the zygote with the help of micro injection and then implanted in the female which gives genetically manipulated offsprings. The factor VIII is isolated from the milk of transgenics and used to treat haemophilia. Transgenics with human beta-globulin gene produce human hemoglobin in their blood.
Xenotransplantation is the process of transplantation of animals organs to human system. Some attempts have been made for the transplantation of pig organs to humans due to their similar sizes as in human. But human body rejected the transplants. This is called hyperacute rejection.
Transgenic Birds - Some blastocytes are transfected with desired gene and introduced to blastocoel of irradiated eggs. The eggs hatch into chimeric chickens. If the blasocytes entered the germ line, the chimeric chicken breed transgenic chickens. These chickens are resistant to Avian leukosis virus (ALV). They have good meat quality and eggs having less cholesterol and fat.
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