NON-DISJUNCTION OF SEX CHROMOSOMES 591 



There is no question of association here, for the white and pink 

 are in different chromosomes, the sex and the third. 



The interpretation of these results is as follows: among the 

 Pi pink females used there was at least one female which formed 

 some eggs in a non-disjunctional manner with respect to the sex 

 chromosome, but not with respect to the second and third chro- 

 mosomes. The duplex sex chromosome of the pink female con- 

 tained only non-mutated genes.'' Wherefore the female resulting 

 from the fertihzation of the two-X egg would be indistinguishable 

 from the other Fi females, irrespective of the character of the 

 sperm. But the no-X egg, if met by a one-X sperm would pro- 

 duce a male exhibiting all the sex chromosomal characters of 

 the Pi male which supplied the chromosome. Since the Pi male 

 was white and miniature, these characters were the ones which 

 showed in the three such males of this experiment. 



If this non-disjunction involved the second chromosome, then 

 in Fi there might appear some black females and males, which 

 was not the case. The white miniature males, moreover, should 

 be black but simplex, and in the next generation there should 

 result a great overproduction of blacks, which was not observed. 

 A similar disturbance in the reduction of the thhd chromosome 

 would have disturbed the F2 ratio from that observed. 



The case just cited illustrates the production and composition 

 of the patroclinous males. The next case gives evidence upon 

 these points for the females. I crossed some white pink females 

 to some eosin vermilion pink males. The expectation in Fi is 

 white pink males and white-eosin compound pink females hetero- 

 zygous for vermilion. This cross is reported in this number and 

 an analysis given by Morgan and Bridges. Of the factors con- 

 cerned, the third chromosomal pink entered the zygote from both 

 sides so that all flies in this experiment are pink. White and 

 vermilion are sex chromosomal and so in expectation all the sons 

 of the white not-vermilion mother are white and likewise not- 

 vermilion. White and eosin are allelomorphic to each other, that 

 is, they occupy the same locus in the sex chromosome. Of the 

 two homologous sex chromosomes of the Fi female the mater- 



* Except the gene for non-disjunction itself, as will appear later. 



