Robertsonian translocations introduced into an island population of house mice

In April 1982, 77 house mice from the Orkney Island of Eday were released by R. J. Berry and his associates on the Isle of May, Firth of Forth. The Isle of May had a standard house mouse karyotype (2n = 40), while those from Eday are homozygous for three centric fusions (2n = 34). Within 18 months of introduction (September 1983), each centric fusion had increased in frequency from an estimated starting value of 8% to a value close to 50%, and they were segregating in accordance with Hardy–Weinberg expectations. In essence, the transformed population was behaving as a panmictic unit. The frequencies of introduced chromosomes had apparently stabilized by September 1986 with values around 65% for all three fusions. The cytogenetic data obtained in the Isle of May introduction experiment accord well with data for single gene loci (represented by allozyme data) and morphometric data. Male Eday–May F1 hybrids were found to have a low frequency of non-disjunction (13%). This study is unusual because the successful introduction of mice into an established population, and the introgression and stabilization of three centric fusions, could not have been predicted from previous studies on the mouse.