Transgenics embryo implantation

One method, first successfully attempted in mice in the 1970s, uses newly fertilized eggs. The researchers use a very fine needle to inject the desired DNA into the area containing the DNA from the sperm, before the sperm and egg have fused. The injected DNA may become part of the sperm DNA. After fusion has occurred, the fertilized egg is allowed to develop into a two-cell embryo, which is then implanted into a female mouse. If the embryo attaches to the uterus, the pregnancy will go forward and healthy pups, or baby mice, will develop. Successful development of transgenic mice is not certain, because only one-third of the embryos placed into a mouse uterus develop into live animals, and only a few may carry the transgene and produce the desired protein. 

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