96 



AN INTRODUCTION TO MODERN GENETICS 



united elsewhere they may be pulled apart in division by the separation 

 of the two centromeres to opposite poles. 



The origin of these chromosome abnormaUties is probably by 

 breakage while the chromosomes are lying in random loops in contact 

 with one another. Their production is gready increased by treatment 



II 



-0-1 



II 



1-I07-5- 



11 II 



V 



-44 

 (Si) 



-26-5 

 (h) 



(rui 

 — 



III III 



0- 



26-5- 

 (h) 



(St) 



44- 

 -48- 



-58-5- 



<5S) 



-70-7- 



(€) 



-106- 



IV IV 



Fig. UU. Cytologicai and Genetical Evidence of a Translocation. — A 



translocation, known as the "Star Curly" translocation, appeared in X-rayed 

 D. melanogaster. It was found by linkage studies that the "left" end of one 3rd 

 chromosome had been broken between the loci of scarlet (st) and pink (p) and 

 the fragment attached to the "right" end of a 2nd chromosome. The cytologicai 

 findings were in accordance with this, as may be seen from the mitotic metaphases 

 shown. 



(From Painter and Muller.) 



of the parent organisms with high frequency radiations {X rays, y rays) 

 or electrons (^ rays). 



Genetic analysis of a chromosome abnormahty enables one to find 

 what section of the chromosome map has been shifted, e.g. by deter- 

 mining which genes are suppressed by a dupUcation.^ The first fact to 

 notice is that a translocation or deletion affeas a set of genes contained 

 ^ Bridges 1917, 1919a. 



