Translocations 



407 



pole with equal frequency, these plants will be semi-sterile. The 

 original homozygous, noninterchange line is sometimes referred 

 to as the "standard" type, following the practice in Datura. 



Apparently reciprocal translocations have occurred in a num- 

 ber of species and races of Datura. Blakeslee and his co-workers 



>— / 



Viable 



a 



Inviable 



Fig. 111. The three possible orientations in rings of four chromosomes 

 resulting from a reciprocal translocation. In (a) two viable types result; 

 one has the two interchange chromosomes and the other the two noninter- 

 change chromosomes. In (b) and (c) all the gametes are inviable for all 

 carry a deficiency and also a duplication. 



have found that many different types of interchanged chromo- 

 somes exists in six species. They were originally called "races," 

 but they are now referred to as "prime types." The methods of 

 analysis of these types and of identification of an unknown are 

 interesting. The ordinary species of Datura have twelve pairs 

 of chromosomes, each pair designated by two numbers, each of 

 which represents the end of a chromosome. Thus in prime type 

 1 (formerly line 1) of D. stramonium, the twelve pairs of homolo- 



