Embryo banks in the future of developmental genetics.

HE initial discovery by POLGE, SMITH and PARKES (1949) that glycerol aff ords protection to spermatozoa during freezing and thawing subsequently led to the development of semen banks which have greatly facilitated livestock improvement especially in the cattle breeding industry. However, until recently, the few attempts to preserve mammalian embryos by freezing have been relatively unsuccessful (see reviews by AUSTIN 1961 ; HAFEZ 1969,1971 ; WHITTINGHAM 1973a). The major advantage of preserving the mammalian embryo is that the embryo, unlike the spermatozoan or oocyte, contains the complete genome of the individual to which it will give rise and this can be propagated in a foster mother of unknown genetic background. The major drawback is the limited number of embryos that are available and therefore the freezing technique must have survival rates approaching 100% if it is to have any practical application. Such survival rates are extremely high when compared with those for spermatozoa frozen under optimal conditions (30-50% SHERMAN 1969). Nevertheless, the ability to preserve viable embryos at low temperatures has practical applications in genetics, developmental biology, and the animal breeding industry as well as contributing to the understanding of basic cryobiology. The purpose of this presentation is to outline a successful technique for the low temperature storage of embryos and to describe its application in the field of genetic research especially mouse genetics.