INDUCED CHROMOSOMAL ALTERATIONS IN MAIZE 



1305 



The products of interchange of single strands at a double-strand 

 stage are more complex than those expected for breakage and reunion 

 of whole chromosomes. In the case of a double-strand chromosome 

 looped back upon itself (intrachromosomal interchange), one strand may 

 be interchanged with itself or with its sister strand. If we designate 

 the broken ends in their original order as ab cd, h and c being the ends 

 of the intermediate or loop section, the broken ends may become attached 

 in the two new combinations ac, bd and ad, be. The chromosomes 

 recovered are listed in Table 1. Combinations without spindle attach- 

 ments or with double spindle attachments become lost. In the duplicate- 

 deficient chromosomes, one end of the chromosome is deficient but is 

 replaced by a duplication of the other end. The internal duplications 

 would be of the constitution abcbcd. 



Table 1. — Chromosomes Recovered from Intrachromosomal Interchange of 



Strands at Double-strand Stage 

 Original sequence of parts ab cd 



In the case of interchange between different chromosomes, the 

 sister strands are equivalent. If each segment with spindle attachment 

 unites with the terminal segment from the nonhomologous chromosome, 

 the four resulting chromosome strands may be designated 1, P, 2, and 2^ 



