a1 MRG Radiobiology Unit, Harwell, Didcot, OXON 0X11 0RD
The frequency of adjacent-2 disjunction in mice carrying the reciprocal translocation T(9; 17)138Ca was studied by mating together animals heterozygous for the translocation and carrying different recessive marker genes, using Tt for chromosome 17 and cwcw for chromosome 9. The proportion of marked young arising from adjacent-2 disjunction varied according to the markers carried in the two parents. When the female carried Tt the frequencies of marked young were always higher than when non-T females were used, and when Tt and cwcw were carried in the same parent there was a shortage of marked young obtaining both copies of the proximal region of chromosome 17 from the father. Both these effects were regarded as probably another example of the phenomenon discovered by Johnson, of inviability of young lacking a maternal homologue of a certain region of chromosome 17. There were other variations in frequency of marked young, among crosses using non-T females, which may have been due to differences in transmission ratio of male gametes carrying various t-haplotypes or to true variations in frequency of adjacent-2 disjunction.
(Received November 08 1976)