4.96" GENETICS OF SOMATIC CELLS 



bodies in rodent species remains to be verified, even though resting cells of female 

 tissue appear more chromatic. 769 The distinctness of the heteropycnotic behavior of 

 the XY bivalent and its respective mitotic analogs is quite striking. 966, 1459 (See 

 figure 59.) 



Ohno, Kovacs, and Kinosita 967 and Ohno and Hauschka 963 related differential 

 heteropycnotic alterations to representing only one of the X chromosomes in female 

 cells of the rat and mouse. A recent assessment and acceptable explanation of Tjio 

 and Ostergren's 1321 observation of so-called heterochromatic stimulation by the viral 

 agent of mammary adenocarcinoma 963 has brought the mitotic sex elements in the 

 mouse to light for the first time in over a decade of critical observation by numerous 

 cytologists. The great majority of reports on murine chromosomes to date have failed 

 to be concerned with the identification of sex elements. At present, the status of sex 

 chromosomes in practically all of the experimental tumors of the rat and mouse remains 

 virtually unknown. 781876 A similar situation does not exist in the Chinese hamster, since 

 the sex chromosomes have been identified for some time. The distinctness in structure, 

 function, and evolutionary significance of the sex chromosomes of normal and malig- 

 nant cells have been reviewed by Yerganian et a/. 1463 In the Chinese hamster, the X 

 and Y chromosomes are readily identified by characteristic features and the more 

 slender appearance of heterochromatic arms, even at magnifications as low as 200 

 times. The individuality of the A' chromosome in both sexes is so readily seen that the 

 duality of the X chromosome in the female is prominently brought to mind (figures 63, 

 64, and 65) . Additional genetic and physiologic evidence for the duality (A^ and X 2 ) 

 of the A'-chromosome pair in the female Chinese hamster has been presented else- 

 where. 1316, 1459, 1461, 1464 The possibility that a triheterosomic somatic sex expression 

 exists in many other species, including man, is most encouraging in the light of more 

 recent morphologic evidence from this laboratory (figure 69). 



Although numerous photomicrographs of normal and abnormal human comple- 

 ments have appeared in the literature recently, few of the authors selected a pair of 

 metacentrics in Group 6-12, which this author and his colleagues consider either as 

 being consistent from paper to paper, or as counterparts of the X 1 and X 2 chromosome 

 of the Chinese hamster. Figure 69b is of a normal male, showing the X 1 quite clearly 

 due to its partly allocyclic nature. A slight fuzziness is apparent and, at times, 

 exaggerated when the chromatids have not separated sufficiently. Figure 69A is that 

 of a normal (pregnant) female showing the A' x and X 2 chromosomes. The dual nature 

 of the X pair is quite apparent, even when following staining procedures outlined by 

 others. It is most puzzling to view these structures in human cells as similar to the 

 scheme in the Chinese hamster. A triheterosomic somatic expression or duality of 

 the A' chromosomes is also noted in malignant cells cultured from a Wilms' tumor and 

 an ependymoma (Yerganian and Kato, unpublished data). 



Autoradiographic procedures to reveal the course of tritiated-thymidine labeling 

 of chromosomes have been readily adapted to known mammalian chromosomes by 

 Taylor 1316 and Yerganian and Grodzins (unpublished data). The differential uptake 



