36o 



PERMANENT HYBRIDS 



Homozi/^ous 

 I Sex 



Sex 



Fig. 112. — Pairing of chromosomes in the two sexes showing parts of 

 X and y that are homologous similarly hatched and stippled, 

 parts of X that are not represented in Y blank, and parts of Y 

 not in X black. I, Humulus lupulus, simple type. II, H. 

 japonicus, simple type (fragmentation heterozygote) . Ill, H. 

 lupulus, with male as interchange heterozygote having X^, Yj, 

 X2 and Ya chromosomes, corresponding to segments BXA, AQ, 

 QP, PY \cf. text). Note. — Types I and II are common in 

 plants and animals. The centromere being median in the 

 X^ the two X chromosomes in the homozygous sex can form 

 chiasmata in one or both arms to give a rod or a ring. From 

 type II the chain of five is derived as the chain of four is derived 

 from type I, 



