PART 11. NEW DATA. 

 WHITE. 



(Plate II, figure ir.) 



The recessive character white eye-color, which appeared in May 

 1910, was the first sex-Unked mutation in Drosophila (Morgan, igioa^ 

 1910^). Soon afterwards (June 1910) rudimentary appeared, and the 

 two types were crossed (Morgan, 1910c). Under the conditions of 

 culture the viability of rudimentary was extremely poor, but the data 

 demonstrated the occurrence of recombination of the factors in the 

 ovogenesis so that white and rudimentary, though both sex-linked, 

 were brought together into the same individual. The results were not 

 fully recognized as linkage, because white and rudimentary are so far 

 apart in the chromosome that they seemed to assort freely from each [ 

 other. 



Owing to the excellent viability and the perfect sharpness of sepa- 

 ration, white was extensively used in linkage experiments, especially 

 with miniature and yellow (Morgan, igiia; Morgan and Cattell, 1912 

 and 191 3). White has been more extensively used than any other 

 character in Drosophila, though it is now being used very little because 

 of the fact that the double recessives of white with other sex-linked 

 eye-colors, such as vermilion, are white, and consequently a separation 

 into the true genetic classes is impossible. The place of white has been 

 taken by eosin, which is an allelomorph of white and which can be 

 readily used with any other eye-color. 



The locus of white and its allelomorphs is only i.l units from that 

 of yellow, which is the zero of the chromosome. Yellow and white 

 are very closely linked, therefore giving only about one cross-over per 

 100 flies. 



All the published data upon the Unkage of white with other sex- 

 linked characters have been collected into table 65. 



RUDIMENTARY. 



Rudimentary, which appeared in June 1910, was the second sex- 

 linked character in Drosophila (Morgan, 1910c). Its viability has 

 always been very poor; in this respect it is one of the very poorest of 

 the sex-linked characters. The early linkage data (Morgan, 1911(3) 

 derived from mass cultures have all been discarded. By breeding from 

 a single Fi female in each large culture bottle it has been possible to 

 obtain results which are fairly trustworthy (Morgan, 191 2g; Morgan 

 and Tice, 1914). These data appear in table 65, which summarizes 

 all the published data. 



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