238 THE THEORY OF THE GENE 



bracon. The common type has black eyes. A mutant male 

 with orange eyes appeared in the cultures. Crossed to 

 black-eyed females, there were produced by parthenogen- 

 esis 415 black-eyed sons, and from fertilized eggs 383 

 black-eyed daughters. 



Four of these (Fj) daughters, when isolated, produced 

 parthenogenetically 268 black-eyed males and 326 orange- 

 eyed males and no females. 



Eight other F x daughters (from the original orange 

 male) were mated with their F, brothers. There were 

 produced 257 black-eyed sons, 239 orange-eyed sons, and 

 425 black-eyed daughters. 



The original mutant orange-eyed male, when bred to 

 his Fj daughter, gave 221 black males, 243 orange males, 

 44 black females, and 59 orange females. 



These results are expected on the hypothesis that the 

 male is haploid and comes from an unfertilized egg. The 

 gene for orange eyes and that for black eyes separate in 

 the germ-cells of the hybrid mother when her germ-cells 

 mature, half of the gametes then have one kind of gene, 

 half the other kind. Any pair of genes in any pair of chro- 

 mosomes will give the same result. 



The reciprocal cross was also made, namely, an orange 

 female was crossed to a black male. Eleven such matings 

 gave 183 black daughters and 445 orange males, as ex- 

 pected ; but twenty-two matings gave, in addition to 816 

 black females and 889 orange males, 57 black males. The 

 occurrence of these black males calls for a different ex- 

 planation. They have obviously come from eggs fertilized 

 by a black-producing sperm. A possible explanation 

 would seem to be that the haploid sperm-nucleus has de- 

 veloped in the egg, and has given rise to those parts from 

 which the eyes at least have come. The rest of the egg 

 might then get its nuclei from the haploid egg-nucleus. 

 There is, in fact, some evidence that this is the correct 



