A simple and convenient method for preparing chimeric animals from embryonic stem (ES) cells.

Gene targeting in embryonic stem (ES) cells followed by preparation of chimeric animals is the most effective method to study the function of a gene during development and differentiation. Here, we describe a cost effective and convenient method to produce chimeric animals. Cryopreserved 8-16 cell mouse embryos were aggregated with ES cells in microwell petridishes (Khillan & Bao, 1997) to obtain blastocysts.