Regulation of Gene Action — Molecular Basis in Higher Organisms 

 SEGMENT CHROMOSOME B 



493 



PUFF 



POST- PUFF 



50 



figure 40-1. Puffing and unpuffing in a region of a salivary gland chromosome 

 of Rhyncosciara. {Courtesy of G. Rudkin.) 



3. All the cells in certain testicular tubes 

 of the grasshopper Melanoplus cliffer- 

 entialis normally disintegrate and lib- 

 erate large quantities of DNA. :; 



4. The oocyte of a newt appears to have 

 in its nucleoplasm and nucleolus DNA 

 — unassociated with the nucleolus or- 

 ganizer — which presumably is not re- 

 tained in the nucleus. 4 



5. A similar situation is reported "' in the 

 oocyte of the dipteran Tipula: Within 

 this cell's nucleus is a body which con- 

 tains about 50 per cent of all the nu- 

 clear DNA present. Not only is this 

 DNA synthesized at a different time 



a See A. Lima tie Faria and T. Nordqvist ( 1962). 



4 See M. Izawa, V. G. Allfrey. and A. E. Mirskv 

 (1963). 



5 See A. Lima de Faria (1962). 



from the DNA in the chromosomes, 

 but this body and its DNA contents 

 disappear at diplonema. 

 6. Germinating wheat seeds and growing 

 roots of wheat and corn contain a 

 double-stranded DNA of low molec- 

 ular weight (10"') which shows turn- 

 over; that is, it is metabolically labile. ,; 

 Such DNA differs from stable, high 

 molecular weight DNA by its higher 

 G + C content. 



Though it may be concluded that DNA 

 is sometimes released to the cytoplasm, no 

 data from the studies mentioned indicate 

 that this material has any of several known 

 or assumed properties of genetic material 



See M. Sampson, A. Katoh. Y. Hotta, and H. 

 Stern (1963). 



