Invited commentary: cryopreservation as a tool for the study of selectively bred lines in rodent behavioral genetics.

Cryopreserved embryos should survive centuries. Upon rederivation, in vitro survival is high. Upon reimplantation, in vivo survival is substantial. Genetic stability of the embryos at -196 degrees C is theoretically absolute for several decades and likely high for centuries. Cryopreservation and rederivation services are available at a reasonable cost from commercial vendors. Preservation of a sufficient number of embryos can serve as an insurance policy against loss of the lines from several causes. In addition to the protective utility of a single banked sample, repeated preservation during the course of selection offers several advantages. Correlated responses to selection which appear late in selection may be verified by use of a cross-sectional experimental design to take a "snapshot" of the gradually developing response. After attainment of the selection limit, a generation may be chosen retrospectively which represents the best compromise between maximizing response and minimizing inbreeding irrelevant to the selected trait. Estimates of changes in gene frequencies could be derived from molecular biological analyses. An example of such an experiment in progress employing embryos from the COLD and HOT selected mouse lines is discussed.