A New Marker for Chromosome Studies in the Mouse

Abstract

THE mouse is one of the best mammals for genetic and cytogenetic investigations. Unfortunately, its value for cytogenetic research is restricted because all forty chromosomes are acrocentric. Their sizes range in the ratio of 5 : 2 (longest to shortest) with relatively little difference other than length to help in identification. At the first metaphase stage of meiosis, twenty bivalents are normally formed and this pairing is commonly used to correlate abnormal configurations with specific chromosome changes. It is obvious, however, that cellular markers (cells with a visible different karyotype from the normal) would be useful for transplantation experiments and work on carcinogenesis or radiation chimeras. Some translocations induced in mice by X-irradiation have been used as such cellular markers^1,2.