[Interspecies chimeras of mammals]

Chimaeras between closely related and distant mammalian species were obtained during the last decade using the aggregation and injection methods. In the chimaeras between the closely related species Mus musculus--M. caroli, the cell clones of both parental species are equally represented; such chimaeras are fertile and their development does not differ from that of intraspecific chimaeras. But in the chimaeras between distant species mouse--rat or sheep--goat a selective predominance of cells with one genotype over those with another was noted. This leads to the total elimination of cell populations with one genotype, rat in particular in the mouse--rat chimaeras, or, possibly, to the sterility of the sheep--goat chimaeras.