SEX DETERMINATION 



shown (P. W. Whiting and A. R. Whiting, 1925; 

 A. R. Whiting, 1926, 1927, 1928a) that "patroc- 

 linous" males were really of biparental inheri- 

 tance, receiving dominant traits of both par- 

 ents. Genetic search was then made for a gene 

 that they might possess in the simplex condi- 

 tion, occupying an odd X chromosome or a dif- 

 ferential X region in one of the pairs. No such 

 gene was found. Later cytological work (Torvik- 

 Greb, 1935) indicated no visible difference be- 

 tween the ten pairs of chromosomes of these bi- 

 parental males and the ten pairs characteristic 

 of females. According to the principle of gen- 

 ie balance, if the genetic complex of the fe- 

 male were merely that of the male doubled, the 

 ratio of male-producing to female-producing 

 genes should remain the same. There should then 

 be but one sex, the male, because any multiple 

 of the haploid complex would make but a slight 

 change in size or proportion of parts, not af- 

 fecting such a radical transformation as is in- 

 volved in sex difference. 



In 1933 (P. W. Whiting, 1933e,f) the hypoth- 

 esis of complementary factors v;as suggested and 

 shortly thereafter proved true by sex-linkage. 

 According to this hypothesis the female is het- 

 erozygous for a pair of sex factors, called X/Y 

 at the time, and she produces two kinds of hap- 

 loid males from unfertilized eggs, X and Y. 

 Mating with a closely related X male gives dip- 

 loid zygotes, male-producing X/X, female-produc- 

 ing X/Y, and male-producing Y/Y. The male-pro- 

 ducing homozygotes are much less viable than 

 the female-producing heterozygotes , accounting 

 for the low frequency of diploid males. 



A supplementary hypothesis of differential 



93 



