121 HEAT SHOCK TO PIG OOCYTES DOES NOT INDUCE APOPTOSIS BUT REDUCES EMBRYO DEVELOPMENT

(age: 8th–19th day) out of which 22 proved to be chimaeric and 3 were adults. Two of these animals were albino but had the triploid component in several internal tissues; both were fertile. The third animal, a male, was an overt chimaera. It turned out to be infertile (no sperm in the ejaculate; testes small and deprived of germ cells). The infertility of this individual is puzzling because the FISH studies with the help of X and Y chromosome painting probes proved that the diploid component was XY and the triploid component was XXX. The results of our study indicate that the rate of postimplantation development of 2n-3n chimaeric embryos is normal or only slightly retarded. Developmental stage of chimaeric embryos was assessed by comparison of their external morphology with normal diploid embryos of equivalent post-coital age according to the descriptions given by Theiler K (1972 The House Mouse, Springer-Verlag, Berlin). With the exception of one embryo lacking both eyes (but otherwise looking quite normal) no other morphological abnormalities were observed. Comparison of the contribution of both components to the fetal and extra-embryonic tissues at the consecutive foetal stages has shown that participation of triploid cells slightly but steadily decreased in all tissues examined. However, the presence of triploid cells in mouse chimaeras was compatible with their normal postnatal development to adulthood.