Cell lines are often taken from an ear and frozen in special sauce so that the cells can be maintained alive at -80c so that embryos can be made from them through a variety of techniques. That's a close enough definition for layman but if you want a real definition, probably just google it. For instance if you have a valuable animal, you call your cloning vendor, they send you a kit and you put some ear in it according to directions and ship to them. I don't know for sure but it probably needs to be shipped in a shipper with liquid nitrogen in it. They probably then do some things in the lab, ie make the cells grow and split into containers and frozen. Above is big fat guess. You can look it up at transova probably.