DNA Loss during Robertsonian Fusion in Studies of the Tobacco Mouse

Abstract

THE centric fusion of two telocentric chromosomes to form a metacentric chromosome, described by Robertson¹, is one of the basic mechanisms for altering the karyotype of eukaryotes. In conjunction with other processes, such as geographical isolation, it is frequently one of the initial steps in the formation of new species. Electron microscopy of mammalian chromosomes has suggested that both of the centromere regions may be retained during the fusion process². A similar conclusion can be drawn on the basis of staining of the centromeric heterochromatin³. In spite of the retention of these regions it is likely that the fusion process is basically a reciprocal translocation event resulting from a crossover within the chromatin fibres that go to make up the centromeric region. The reciprocal product is presumably lost as it is too small to possess a kinetochore.