Creating a transgenic mouse traditionally involves modifying stem cells, transferring them to an embryo, transplanting the embryo into a surrogate mother, and breeding the resulting mosaic mouse.

“the way it worked is that you would start with stem cells for mice you would modify these stem cells and then you put the stem cells back into a embryo and then you transplant the embryo into a a mouse that the embryo can develop into a full um develop into fetus and then be born as a new mouse that is a very long process and then once the mouse is born usually that Mouse does not have 100% of that uh genetic modification so the mouse is called a mosaic and then you have to take that Mouse and breathe the mouse again with another mouse and hoping that um that the Mosaic part is the one that gets expressed and transed basically try to concentrate the Mosaic portion of it”