RESTORATION OF THE MENDELIAN TRANSMISSION RATIO BY A DELETION IN THE MOUSE-CHROMOSOME-1 HSR

The house mouse, Mus musculus, harbours a variable cluster of long-ran ge repeats in chromosome 1. As shown in previous studies, some high-co py clusters such as the MUT cluster are cytogenetically apparent as a homogeneously staining region (HSR) and are associated with a distorti on of the Mendelian recovery ratio when transmitted by heterozygous fe males. The effect is caused by a decreased viability of +/+ embryos. I t is compensated by maternal or paternal MUT. In this study, a deletio n derivative of MUT, MUTdel, shows normal transmission ratios and no c ompensating capability. In this respect, MUTdel behaves like a wild-ty pe cluster. Hence, both properties - transmission ratio distortion and compensating capability - map to the deleted region. The deletion com prises three-quarters of the MUT HSR and does not extend to the neares t markers adjacent to the HSR.