502 GENETICS OF SOMATIC CELLS 



moderately populated culture. In general, fixation before 48 hours or before cells 

 stretch out and divide at least once, leads to unfiattened, dense, rounded mitotic 

 figures. The cell which has divided previously appears to be more satisfactorily 

 flattened with chromosomes dispersed. This is particularly true when neighboring 

 cells are still in the initial phases of adapting to the new surface of the present flask. 



Both air-dried and wet squashes should be tried on new tissues as a means of 

 judging their adaptability to both procedures. Elasticity of the cellular membrane may 

 play some role in the degree to which the cytoplasm will respond to hypotonicity and 

 subsequent spreading. Variations in the utilization of cations by different types of 

 cells may be also instrumental in predicating the type of response to the technique of air 

 drying. A most provocative observation is the excellent preparations obtained by wet 

 squashing normal clonal derivatives and SE polyoma-induced sarcoma that have an 

 extra chromosome III or involve translocations within the heterochromatin (Yerganian, 

 unpublished data). It is quite certain from present unpublished observations that the 

 Y chromosome of the Chinese hamster is not essential for regulating cell cytoplasmic 

 volume or plating efficiency. However, this observation may eventually have some 

 application in other connections. 



The existence of quasi-diploidy or false diploidy in normal cells of other species 

 remains to be fully disclosed. The frequency of quasi-diploid or subdiploid clones of 

 the Chinese hamster, lacking the X 2 or Y chromosomes, is much higher than that 

 expected to occur randomly and to involve the 1 1 chromosomes. Delayed division or 

 formation of the sister chromatids during replication of the entire length of hetero- 

 chromatin or the X 2 and Y chromosomes appears to be a satisfactory explanation for 

 the outright loss of these heterochromosomes from viable cells. Likewise, extensive 

 deletions of the heterochromatic long arm of the X 1 are often noted in viable cells and 

 clones. 1463, 1464 Since the long arm of the X 1 is also delayed during the asynchronous 

 DNA cycle, it too has the tendency to be deleted with greater frequency than that 

 expected. Nevertheless, deleted heterochromatin is not lethal for rapidly proliferating 

 cells in vitro. 



Subsequent implantation of representative malignant sublines into cheek pouches 

 of related animals has revealed that additional heterochromatin favors in vivo propaga- 

 tion. On the other hand, malignant transformations of male fibroblast derivatives is 

 no greater with a modified X X Y than with a modified X x sex mechanism. 1464 The 

 role of sex heterochromatin during the initiation of malignancy remains obscure. 

 However, in reviewing photographs of malignancies arising among Chinese hamsters, 387 

 the long arm of the X 1 chromosome was noted to exhibit increased spiralization similar 

 to that witnessed among parental and clonal isolates of SE polyoma-induced sarcomas 

 and malignant transformations maintained both in vivo and in vitro. In the absence or 

 modifications of the X 2 or the Y chromosome, the long arm of the X 1 displays over- 

 spiralization (reduced length) when the cellular type is capable of forming a trans- 

 plantable tumor in vivo. 



The number of lines propagated in culture and as ascites tumors that retain the 



