484 GENETICS OF SOMATIC CELLS 



Fig. 66. Cloning efficiency of polyoma derivatives of the Chinese hamster. 



Average of 50 per cent cloning efficiency (Puck Technique) displayed by three quasi- 

 diploid, polyoma derivatives of the Chinese hamster. The female derivatives feature 

 variations in the sex mechanism, i.e., XO and XX moA . The male derivative (XY) features 

 four autosomal translocations and an intact sex mechanism. (See figures 64 A and B.) 



Siliconed slides and procedures for permanent preparations 



Invariably, the use of siliconed slides or cover glasses greatly enhances wet 

 squashes. 1174 Silicone-treated paper for wiping eyeglasses is a good substitute, particu- 

 larly when the type of cell studied has adequate cytoplasmic volume. The diploid cell, 

 with minimal cytoplasmic volume, responds more favorably when silicone-treated slides 

 are used. Incidentally, wet-squashed cells are flattened most satisfactorily on siliconed 

 slides, whereas the air-drying procedures employ the principles of hypotonicity, 

 evaporation, and resulting surface tension to spread chromosomes favorably. 



In the event silicone is unavailable, a satisfactory surface may be prepared simply 

 by touching the microscope slide to one's nose. The smear of oil is vigorously rubbed 

 clear with a towel to provide a smooth and water-repellent surface. The use of Kronig's 

 cement is mandatory to assure the proper seal, regardless of the manner in which the 

 slide was wiped clean or prepared. 



In the past, reports of extreme variations in chromosomal number of a given 

 tissue led to considerable debate as to the consistency of modal numbers. The novice 

 must be made aware of this potential pitfall when adapting techniques of chromo- 

 somal preparation to his needs. To insure against loss of chromosomes, it is urged that 

 the principles of air-drying be employed at first. 1322 - 1077 These procedures are 

 especially helpful with normal cells having cellular membranes which are prone to 

 rupture at the slightest pressure. Familiarity with the tissue will then encourage wet 



