[Fecundity and embryonal mortality of four inbred lines of mice, BALB/c, B10.CW, A/Sn CC57W and their hybrids].

The object of this investigation was the potential fecundity of four inbred strains of mice, viz. BALB/c, B10.SW, CC57W, A/Sn and of their different hybrid combinations. The inbred strains studied had different normal ovulation numbers varying from 9,2 to 11,9 and different death-rate of embryos before (10,99-39,49%) and after (9,05-22,47%) the implantation. The numbers of live embryos per female in the strains A/Sn, b10.cw and CC57W were practically equal to one another, but significantly larger than in the strain BALB/c. Interlinear crosses resulted in a considerable decrease of the totalembryonic deathrate, while the normal ovulation number did not undergo any changes. The number of liver embryos in simple hybrids did not differ significantly from that in the maternal inbred strains. Therefore the heterozygosity of embryos did not affect significantly the potential fecunidity of females. The number of surviving embryos per female increased in the cross between the simple hybrids (BALB/cXB10.CW) X (CC57WXA/Sn) to 8,9+/-0,37. This heterosis was the result of the total death-rate of embryos down to 14,89%. Asit is shown by the comparison of the potential fecundity of pregnant females carrrying homo- and heterozygous embryos to that of pregnant hybrid females, the rate of survival of embryos depends more on th