JtJtT 17, 1914] 



SCIENCE 



107 



critical treatment of their own and of others' 

 work, together with a more generous apprecia- 

 tion of the possibility that some other investi- 

 gators might also he gifted with the powers of 

 correct observation. 



Gary IST. Calkins 



SPECIAL ABTICLES 



DIRECT PROOF THROUGH NON-DISJUNCTIOISr THAT 



THE SEX-LINKED GENES OF DROSOPHHiA 



ARE BORNE BY THE X-CHROMOSOME 



In " Non-disjunction of the Sex-chromosomes 

 of DrosopMla," Jour. Exp. Zool., November, 

 1913, the following case was presented: 



1. In certain strains involving sex-linked 

 characters, females arose which could not be 

 explained upon the ordinary mechanism of 

 sex-linked inheritance. These females were 

 maternal in appearance, showing those sex- 

 linked characters which the mother showed, 

 hut no influence of those borne by the father. 



2. Breeding results showed that genetically 

 as well as somatically these exceptional fe- 

 males were exact duplicates of their mother in 

 that they carried no sex-linked genes intro- 

 duced by the father. 



3. Such exceptionally produced females in- 

 herit directly from their mother the power of 

 producing like exceptions; for these females, 

 in turn, gave in Fj when outcrossed to any 

 male, five per cent, of daughters like them- 

 selves somatically and genetically. The re- 

 maining daughters are, in appearance, of the 

 types expected on normal sex-linkage. 



4. Exceptionally produced females gave in 

 Fj a class of sons (five per cent.) complemen- 

 tary to the matroclinous daughters in that 

 these sons both somatically and genetically 

 were purely paternal, having no sex-linked 

 characters introduced by the mother. 



5. The entire set of sex-linked genes of the 

 mother, or the entire set of sex-linked genes of 

 the father, appeared without addition or loss 

 in the matroclinous daughters or patroelinous 

 sons, respectively. This result was independ- 

 ent of the particular composition of the mother 

 or father and held when the mother was mated 

 to any male. 



6. The exceptional Fj males (patroelinous) 



when outcrossed to unrelated females did noi 

 give rise to exceptions in Fj. 



7. By breeding in each generation from the 

 exceptional daughters a " pseudo-parthenoge- 

 netic " line was maintained in which a given 

 sex-linked constitution was handed down in- 

 definitely from daughter to daughter. 



8. The exceptional daughters resulted from 

 the fertilization of an egg of the mother by a 

 normal sperm from the father, as was proved 

 by the introduction into the exceptional 

 daughters of non-sex-linked genes from the 

 father. The inheritance was uniparental with 

 respect to sex-linked genes, and biparental and 

 quite regular with respect to non-sex-linked 

 genes. 



9. The cytological work of Miss Stevens was 

 referred to as showing that in DrosopMla the 

 female has two X-chromosomes and the male 

 an unpaired X. (See, however, section 17.) 



The explanation advanced for this series of 

 facts was that the sex-linhed genes were home 

 hy the X-chromosome, and that ten per cent, 

 of the eggs of the exceptional females retained 

 hoth X-chromosomes or, conversely, lost hoth to 

 the polar hody. 



It was suggested that the cause of the non- 

 disjunction was itself a sex-linked gene. 



Work which has been carried out since the 

 previous paper was published enables me to 

 add the following points: 



10. Half of the expected class of daughters 

 from a non-disjunctional female by any male, 

 inherit directly from their mother the same 

 power of producing five per cent, of matro- 

 clinous daughters and patroelinous sons. For 

 example, white non-disjunctional females 

 mated to wild males gave in F, the following : 



Expected classes. Exceptions. 



95 % of both sexes. 5 % of both sexes. 



"Wild type ? ; white c?. White $ ; wild type cJ. 



HaK of the wild-type daughters (aU were 

 heterozygous for recessive white) when out- 

 crossed to barred males (barred is a dominant 

 sex-linked character) gave exceptions as fol- 

 lows: 



Expected classes. Exceptions. 



95 % of both sexes. 5 % of both sexes. 



Barred ? (2) ; wild type Wild type ?; barred d'. 

 (?(1); white d' (1). 



