chromosome aberrations in Tradescantia 719 



Description of Plate I 



Photomicrographs of Tradescantia microspore chromosomes showing the major 

 types of aberrations induced by ionizing radiations (from Sax, 1940). Figures A-F 

 are chromatid aberration types; Figs. G-0 are chromosome aberration types. (Repro- 

 duced by permission of the author and the editor of Genetics.) 



Fig. A. Untreated. Six normal chromosomes at metaphase. 



Fig. B. An isochromatid break at metaphase. Acentric fragment (U-shaped) at left. 



Fig. C. Similar isochromatid aberration at anaphase. Partially straightened frag- 

 ment to right. 



Fig. D. Symmetrical chromatid interchange at metaphase. 



Fig. E. Asymmetrical chromatid interchange (at top) and a chromatid break (center). 



Fig. F. Chromatid break at anaphase, shortened arm and acentric fragment visible 

 at upper center. Also probable chromatid-isochromatid intrachange giving duplica- 

 tion-deficiency chromatids (to left). 



Fig. G. A chromosome break (upper center) and a chromosome interstitial deletion 

 (to right). 



Fig. H. An asymmetrical chromosome interchange (dicentric); paired acentric frag- 

 ments at lower right. 



Fig. I. An asymmetrical chromosome interchange (dicentric) at upper right, and an 

 asymmetrical chromosome intrachange (centric ring) at lower center. Two pairs of 

 acentric fragments at top, center and left. 



Fig. J. A symmetrical chromosome interchange. 



Fig. K-N. Types of separation at anaphase of asymmetrical chromosome inter- 

 changes (dicentrics) . An interstitial deletion is also present in Fig. N. 



Fig. O. Anaphase separation of an asymmetrical chromosome intrachange as a 

 continuous ring. Somatic nondisjunction ha"s also occurred. 



