THE KARYOTYPE OF THE MOUSE, WITH IDENTIFICATION OF A TRANSLOCATION

Abstract

By using the methods described by Ford and Wooliam and selecting only the most favorable cells for analysis, it is possible to identify consistently in normal mouse cells 4 autosomal pairs, 3 of which show secondary constrictions and differences in size which make them useful as landmarks, and the Y chromosome. Furthermore, even though mouse chromosomes are difficult to classify, it is felt that an approach to a workable karyotype can be made by arranging chromosomes in sequence roughly by size but also in pairs based on morphological similarity. This method seemed to be more realistic and also to lend itself more readily to the detection of differences among different karyotypes than methods based on size alone. The possibility is offered, based on karyotype analysis and the use of satellited chromosomes as landmarks, that the X chromosome may not be, as currently thought, one of the largest chromosomes, but one of medium size instead. The cytological detection of a translocated chromosome is presented; heterozygotes for translocation T190 have one chromosome far longer than any in the normal set, and one smaller. This difference can be detected without karyotyping and thus would serve as a cell marker.