and then:
from Detloff, P. J., J. Lewis, S. W. John, W. R. Shehee, R. Langenbach,
N. Maeda and O. Smithies 1994. Deletion and replacement of the mouse adult
beta-globin genes by a "plug and socket" repeated targeting strategy. Mol Cell
Biol. 14:6936-6943
Lewis, J., B. Yang, P. Detloff and O. Smithies 1996. Gene modification
via "plug and socket" gene targeting. J Clin Invest. 97:3-5