In addition to studying the function of a specific gene by introducing it into cultured cells by transfection techniques, it is also possible to insert specific genes into live animals. These animals are known as transgenic animal models . (Karp, p. 770) A transgenic mouse contains additional, artificially-introduced genetic material in every cell. This often confers a gain of function. For example, the mouse may produce a new protein, but a loss of function may occur if the integrated DNA interrupts another gene. A transgenic mouse is a very useful system for studying the expression (DNA mRNA protein) and function of a specific gene under controlled conditions within the context of a living organism. There are two major methods for creating a transgenic mouse: a) microinjection of DNA constructs into the male pronucleus of mouse zygotes b) introduction of DNA into embryonic stem cells (ESCs) by transfection, followed by integration of the ESCs into the developing mouse embryo. The microinjection technique will be described here, because it is the technique used by
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