Marker Chromosome Analysis of Tetraparental AKR↔CBA-T6 Mouse Chimaeras

Marker chromosome analysis of 18 tetraparental AKR↔CBA/H-T6 chimaeras revealed a great excess of AKR mitoses over CBA mitoses in direct preparations from lymphomyeloid tissues, corneal epithelium, intestinal epithelium and skin (Table 1). The degree of AKR dominance was strongly influenced by anatomical site (Tables 2 and 3). The testes of three out of four XY/XY males contained a marked excess of AKR germ cells and produced a parallel excess of functional AKR gametes (Table 4). Mitotic spreads in mitogen-stimulated cultures of tail blood were overwhelmingly of AKR type in 1972, but less so in 1973 (Table 5). The coat phenotypes, and breeding results from known or presumptive XX/XX females, suggest that AKR and CBA cells were numerically balanced when melanoblasts and oocytes were formed during embryonic development, and therefore that the striking deviations from equality observed in mitotic populations of adult chimaeras arose later by differential proliferation or survival of AKR cells, or both. The low frequency of lymphomas, compared with normal AKR mice, previously reported in these chimaeras cannot therefore be accounted for by insufficiency of AKR cells in the thymus or elsewhere in the lymphomyeloid tissues. One of three lymphomas studied was CBA type. This suggests that the high risk of lymphomatous transformation is not an autonomous property of AKR cells.