No. 631] COLOR CLASSES IN DOVES AND CANARIES 163 



in sex-linkage nor non-disjunction, and which expects no unusual 

 sterility nor the appearance within the crosses made, of other un- 

 recorded exceptions to the normal relation between phenotypic 

 color classes. 



We may take up in order the three hypotheses of partial sex 

 linkage, non-disjunction and factorial change and may compare 

 them on the basis of the experimental results obtained. 



Partial Sex-linkage 

 1. Doves. — The normal result obtained when white male and 

 colored female ring doves are crossed, is colored males and white 

 females. This may be explained as follows : Let W equal a factor 

 for the production of colored plumage and w, a factor allelo- 

 morphic to it for the production of white plumage. The male is 

 FFMM, the female FFMm in formula. W is linked with M in 

 inheritance. 



Forming gametes wFM 

 Zygotes obtained: WwFFMM 

 wwFFMm 



In addition, however, exceptional colored females are produced 

 infrequently and have been recorded by Staples-Browne (1912), 

 and by Strong (1912). These exceptional colored females have 

 been acounted for by Bridges (1913), as follows: 



If in the female the sex-differentiating factor and the factor for 

 plumage color are placed close enough together in the same chromosome 



would cause the two factors which entered in the same member of the 

 homologous pair of chromosomes to lie in different members and hence 

 to segregate to different gametes. 



