Studies on Chromosomes 3 1 



characters takes place in the gamete-formation, and the resulting 

 yellow-bearing gametes unite freely with those bearing the reces- 

 sive color, they do not unite with each other: "Ceux-ci (the 

 yellow heterozygotes) forment bien des gametes de valeur CJ ou 

 AJ, mais ces gametes ne peuvent pas s'unir les uns aux autres pour 

 donner des zygotes ayant les formules CJCJ, AJAJ ou CJAJ; 

 par autre, ils s'unissent facilement a tous les autres gametes que 

 j'ai essay es pour former avec eux des heterozygotes mono- ou 

 dihybrides" (op. cit., p. cxxx). This conclusion is sustained by 

 the fact that the combination Y(G) x Y(G) (CYCG x CYCG in 

 Cuenot's terminology) produces a relative deficiency of yellows 

 in the offspring, as is to be expected. 1 In pairing Y(G) with 

 Y(G), accordingly, the Y-bearing spermatozoa unite only with 

 the G-bearing eggs, and vice versa, which is exactly analogous 

 to the selective fertilization assumed in case of the sex-bearing 

 gametes. Perhaps it may be possible to find a different expla- 

 nation of the facts; but if Cuenot's interpretation be well-founded 

 the case goes far to remove the scepticism which I think one must 

 otherwise feel in regard to a selective fertilization of the gametes 

 in sex-production. 



An examination of the question of dominance involved in the 

 Mendelian interpretation leads to some interesting conclusions. 

 In forms possessing unequal idiochromosomes the sexual formulas 

 would be for the female (m) f and for the male m (/) (/ being the 

 small idiochromosome). Applying the same interpretation to 

 Nezara, where the idiochromosomes are of equal size, the corre- 

 sponding formulas are (m) f and m (/), giving the gametes (m), 

 /, m and (/). Assuming likewise a selective fertilization the facts 

 would be: 



EGGS SPERMATOZOA 



() + (/) = ( m ) (/) producing a male, m(f). 



f + m = mf, producing a female (m) /. 



rfhe deficiency, though constant, is very slight. Cuenot himself seems to consider this a difficulty, 

 but I believe a very simple explanation may be given. With equal numbers of the gametes of both sexes 

 the ratio of yellows to grays should be two to one, instead of three to one as in the typical Mendelian case 

 (since the class YY is missing). If, however, the spermatozoa be in large excess, as they undoubtedly 

 are, all or nearly all the Y-bearing eggs will be fertilized by G-bearing spermatozoa, and vice vena, thus 

 bringing the ratio of yellows (Y(G)) to grays (GG) more or less nearly up to three to one. 



