500 GENETICS OF SOMATIC CELLS 



adapted by A. C. Longwell. A large number of clonal isolates and sublines have 

 either the X 2 or the Y chromosome missing, and apparently the loss does not interfere 

 with cellular viability and function. Measurements such as plating efficiency appear 

 to be affected when heterochromosomes are missing or altered. The X 2 and Y chromo- 

 somes are more similar to one another than the X x is to the AV 459, 1316 in contrast 

 with earlier ideas regarding the origin and function of mammalian sex chromo- 

 somes. 



The loss of sex heterochromatin fails to affect cellular viability, whether it be the 

 whole or part of the long arm of the X x or the entire lengths of the X 2 and Y chromo- 

 somes. Similar situations are, of course, noted in human syndromes. 1026 Thus, sex 

 heterochromatin may be considered essential for normal development of the sexes. 



Malignant transformations in vitro, or similar changes in fibroblast-like derivatives 

 when placed in vivo, have been noted to occur during or immediately following altera- 

 tions in the appearance of the heterochromatic long arm of the X 1 chromosome of a 

 line derived from a male. 1464 At no time has the short arm of the X 1 been noted to be 

 disturbed consistently in a viable normal cell. Although evidence is still lacking, the 

 short arm of the X 1 is probably the most vital complex of euchromatin-heterochromatin 

 in the cell. Its integrity appears to be most essential for cell viability. 



The adult animal exhibits normal antigen-antibody histocompatibility responses 

 for grafts of skin and tumors and metabolic mutants, such as diabetes mellitus. The 

 adults survive well over four years in the laboratory. 1462 Stress reactions following 

 exposure to X irradiation or cortisone, or both, may be accompanied by symptoms of 

 diabetes mellitus and diabetes insipidus depending on the sublines (Yerganian and co- 

 workers, unpublished data). The diabetic animal exhibits the pathogenesis noted 

 clinically. 865, 866 In addition, the biochemical and dental aspects of the disease are 

 equally striking and compare well with human peridontal syndromes (Cohen, Shklar, 

 and Yerganian, unpublished data). Increased alpha-2 serum proteins are currently 

 considered useful in the early detection of potential diabetics. 494 



GENERAL REMARKS 



Although the material reviewed has dealt primarily with rodent specimens, 

 application of these procedures to cells of amphibia, reptiles, birds, and primates is also 

 feasible and results encouraging. Additional information, particularly in the realm 

 of pretreatments, could have been reviewed in greater detail. However, present 

 progress makes it advisable to simplify and eliminate unnecessary technical steps, 

 particularly when additional attention to preparation of media, routines of tissue 

 culture, and, finally, cytology is required. There is little need for the novice to repeat 

 the many time-consuming procedures that have led to the simpler techniques in use 

 today. 



The effectiveness of extended hypotonicity (20 minutes) has proved its value 

 beyond any doubt when employing tissues having numerous chromosomes which are 



