FUSION HETEROZYGOTES 



141 



12 11 W 9 8 7 6 5 4 3 2 I 



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Fig. 46. — Permanent fusion of chromosomes shown by differences 

 between Hesperotettix hrevipennis {A) and different races of H. 

 viridis [B-E). The complements shown are those of males and 

 have a single unpaired sex chromosome {X, or No. 4, v. Ch. IX). 

 A-D, mitosis, polar view. 



A, 



all chromosomes have terminal centro- 



2w = 23 ; 

 meres. 



B and C, 2n = 20 ; three pairs of non-homologous chromo- 

 somes have fused and have median centromeres. 



(In B, X and 9, 11 and 12, both pairs ; in C, 9 and 10, 11 and 

 12, both pairs.) 



D, 2w = 21 ; two pairs have fused. 



E. First metaphase of meiosis in side view ; chromosomes 

 drawn separately, a. The same type as A. b, 2n = 22, X fused 

 with 12. c. The same type as B. d, 2n = 19. 9 fused with 10 

 and II with 12. All these are examples of fusion-homozygotes 

 except in regard to the unpaired X-chromosome which necessarily 

 gives heterozygotes in the male. (From ]\IcClung, 191 7.) 



