Abstract
Chimaeras were produced from highly asynchronous mouse embryos, in which single nucleus of 2-cell embryos (F1×F1;C57BL/6J×CBA) was exchanged with allogenic 2- or 8-cell nucleus (CD-1×CD-1 or BALB×BALB). The pattern of distribution of each component was examined by judging of the coat color in the pups derived from chimaeric embryos after transfer. The proportion of chimaeric embryos developed to blastocyst was 81-96%, and 56%-70% of these embryos give rise to live young after transfer. Seventy percent of the pups which derived from 2-cell F1 embryos receiving single nucleus from 2-cell CD-1 embryos was chimaeric. However the proportion of chimaeras was signifi-cantly decreased and that of colored was significantly enhanced when nucleus from 8-cell embryo was transferred. Similar results were obtained in the chimaeras produced from F1 and BALB embryos. These facts suggest that cells with nucleus from 8-cell embryos were tended to exclude from the ICM. In the male chimaeras, the cells with CD-1 nuclei were predominantly distributed to their germ line, but the cells with BALB nuclei were excluded from it.
