310 CHROMOSOMES IN HEREDITY : PHYSIOLOGICAL 



property, as it is found in the sex chromosomes, is determined 

 genetically and not by the pairs being structurally dissimilar, as a 

 superficial study would suggest. 



The whole of the sex chromosomes are affected in the heterozygous 

 sex where they do not pair at pachytene, whether there is a single 

 X as in some Orthoptera and Nematoda, or both an X and a Y as 

 in the Hemiptera. In the Hemiptera certain fragment chromosomes 



Table 46 



Comparison of Cycles of Differential Condensation in Different 



Organisms 



Hepaticae 

 XY 



Pre-meiotic mitosis. 

 Prophase 

 Metaphase . 

 Meiosis. 

 Leptotene 

 Pachytene . 

 Diffuse stage 

 Diplotene 

 Metaphase I 

 Metaphase II 



+ 

 o 



+ 



+ 



+ 

 o 

 o 



Explanation : O, no differential condensation ; +, over-condensation ; 

 — , under-condensation ; P, the precocious autosome of Stenobothrus, etc. 

 (i) Progressively increasing towards meiosis. 



(2) No precocity, but according to Buchner there is a condensed body 

 attached, which is probably a nucleolus. 

 Cf. Orthoptera : White, 1935 ; D., 1936 d. 

 Marsupials : Roller, 1936. 

 Rat : Roller and D., 1934. 

 Hepaticae : Tatuno, 1933 ; Lorbeer, 1934. 



and, in some Orthoptera, several smaller members of the normal 

 complement, share the property. These are sometimes derived 

 from the sex chromosomes, since they pair with the Y in Metapodius 

 (Wilson, 1909), and with the X in v4/y^/^s (Renter, 1930) (cf. Table 16). 

 In certain species with an anomalous type of meiosis half the 

 chromosome complement is affected (e.g., in Lecanium, Pseudococcus 

 and Gossyparia, q.v.). 

 The property may show itself long before meiosis in the failure 



