1174 



BIOLOGICAL EFFECTS OF RADIATION 



Table 1 



As shown above, the apparent Hnkage observed between genes 

 located in different chromosomes in translocations is due to the inviability 

 of the recombination classes carrying duplications and deficiencies (Fig. 1). 

 This apparent linkage provides a possibility of determining genetically 



sp 



px 



oil 



dp! 



,pr 



± 



m 



+ i= ?= 



Fig. 2. — Determination of the points at which chromosomes are broken in transloca- 

 tions. A translocation carrying female heterozygous for a series of genes (left) is crossed 

 to a male free from the translocation and homozygous for the respective genes (right). 



the loci at which the chromosomes were broken and reattached in trans- 

 locations, provided, of course, the spacing of genes in normal chromosomes 

 is known, as is the case in Drosophila. Translocation females are made 

 heterozygous for a series of genes located in both chromosomes involved, 

 and are back-crossed to normal males homozygous for the same series of 

 genes (Fig. 2). Crossing over takes place between the chromosomes 



