sparrow: cytogenetic effects of ionizing radiations 



75 



ESTIMATED RADS PER HOUR PER NUCLEUS 

 0.5-1.0 10-2.0 1.5-3.0 20-4.0 2.5-5.0 3.0-6.0 3.5-7.0 40-8.0 



160 



140 - 



c/> 120 

 i±j 

 to 

 < 



X 



a. 

 < 



8 



cr 



Q. 

 CO 



liJ 



< 



00 - 



80 - 



60 — 



40 - 



20 - 







10 20 30 40 50 60 70 80 



AVERAGE GRAINS PER DIVIDING NUCLEUS 



90 



100 



6.2 



12.5 



18.7 



25.0 



31.2 37.5 



ESTIMATED DISINTEGRATIONS/ NUCLEUS / HOUR 

 Figure 6. — Increase in chromosome fragmentation in Tradescantia palu- 

 dosa exposed to 1 \xc\ml H 3 -thymidine as a junction of autoradio- 

 graphic grain number over dividing nuclei. 200 or more cells were scored 

 for each point. Disintegrations per nucleus calculated on basis of 1 

 grain per 143 disintegrations. After Wimber (196). 



ionizing track which traverses the strand or strands, and on a great 

 number of other factors. (See sections on chromosome breakage and 

 modifying factors.) 



3. Changes in chromosome number 



Changes in the basic chromosome number vary from the addi- 

 tion or subtraction of one or a few chromosomes to the alteration of 

 whole chromosome sets. Haploidy, triploidy, and tetraploidy have 



