406 Intrachromosomal Aberrations 



organism will be highly fertile. On the other hand, if the passing 

 of alternate or adjacent chromosomes to the same pole is a purely 

 random matter, only about one-third of the spores or gametes 

 will have a complete genome (Fig. Ill, bottom) and, especially 

 in plants, the organism will be only partly fertile. Theoretically, 

 two-thirds of the gametes of such plants will be sterile. In sev- 



FiG. 110. Chromosomes of Rhoeo discolor at the first meiotic metaphase. 

 All the chromosomes are arranged in a complete ring because of numerous 

 reciprocal translocations. (Courtesy of Dr. K. Sax in the Journal of the 

 Arnold Arboretum.) 



eral actual cases, however, only about half the gametes were 

 found to be sterile. Brink, Burnham, Sutton, and others have 

 reported the occurrence of "semi-sterile" or "half-sterile" plants 

 in maize, peas, and other plants (Fig. 112). 



If a translocation heterozygote is self-fertilized, three types of 

 offspring will be produced in a 1 : 2 : 1 ratio. One-fourth of the 

 offspring will be homozygous and will be like the original type 

 without the translocation, whereas one-fourth will be homozy- 

 gous but will be of the interchange or translocation type. Both 

 types will exhibit perfectly normal chromosomal pairing and 

 will be highly fertile. The other half of the offspring will be 

 translocation heterozygotes and will therefore show cross-shaped 

 configurations in zygotene. If alternate or adjacent chromo- 

 somes in this translocation heterozygote can pass to the same 



