Cytogenetics of the mouse.

Abstract

The mouse has a number of favorable attributes for genetic studies. It is a mammal, and its many biochemical and physiological similarities to the human make its study particularly relevant to human genetics and medicine. It is easy to handle and breeds relatively quickly so that as many as a hundred consecutive generations can be studied in one human generation. Many workers are studying the mouse and a large number of genetic markers have been developed (I). Furthermore, inbreeding has been relatively successful, and several hundred highly inbred lines have been produced (2). The virtual genetic identity of mice in an inbred line facilitates many kinds of genetic studies. One of the difficulties in studying mouse genetics, until recently, was the lack of satisfactory methods for cytologic analysis of chromosomes in either mitotic or to a lesser extent meiotic spreads. Formal genetic analysis in higher oganisms, which are diploid, is most effective when the study of genetic markers can be combined with direct study of mitotic and meiotic chromosomes. If giant somatically paired chromosomes were available, as in Drosophila, recogni­ tion of translocations, inversions, and deletions would be quite easy. Recently, evidence has been presented that polytene chromosomes may be present in the markedly polyploid cells of mouse trophoblast (3). There is, as yet, no evidence of somatic pairing, or any indication that a detailed banding pattern is present along these chromosomes, even though their appearance was induced by a treatment, exposure of living cells to actinomycin, known to produce banding of the chromosomes in diploid cells (4). At present the chromosomes in trophoblastic cells, despite their great interest, are not readily accessible for study. The initial development of mouse genetics was limited primarily to recom­ bination analysis. The first autosomal linkage, albino (c) and pink eye (P), was