Genetic transmission of mammary tumour virus in the DBAf mouse strain

MTV antigens were demonstrable by radio‐immunoassay in milk samples from individual DBAf mice, and in samples from (♀B́LB/c × ♂DBAf) F 1 mice. Although some samples collected during the first lactation periods of these mice were virus‐negative, all samples of later lactation periods were virus‐positive. From 75 mice of the [♀(♂BALB/c× ♂ BALB/c× DBAf)]Bc I population, milk samples were collected during one or more lactation periods and tested for the presence of viral antigens; the samples of 42 mice were virus‐positive. In the {([BALB/c ×(BALB/c × DBAf)]) × BALB/c}Bc II population two groups were distinguished. In the first group, the progeny of virus‐positive Bc I mothers, 37 out of 62 mice had detectable levels of viral antigen in the milk. None of the 43 samples from mice of the second group, derived from MTV‐negative Bc I females, were virus‐positive. These data suggest that the presence of viral antigens in the milk of DBAf mice is controlled by a single dominant gene; evidence for linkage of this gene and the albino locus was obtained (recombination percentage: 20).