No. 631] COLOR CLASSES IN DOVES AXD CANARIES 171 



among their gametes some that were WFM instead of wFM the 

 following result would be obtained in a cross between one of 

 them and a colored female. 



: wFM commonly 

 WFM exceptionally 

 (1) WwFFMM = colored r 



(4) WtvFFMtii = colored females (exceptionally) 



Of the two exceptional zygotic classes (3) and (4) only the 

 latter represents a distinguishable phenotypic difference. The 

 other (3) would be merely individuals homozygous for the factor 

 W and therefore indistinguishable, except by proper breeding 

 tests, from the common heterozygous class (1). Such tests have 

 not been reported on as yet by investigators in whose stock, class 

 (4) individuals; have appeared. The point to be emphasized, 

 however, is that the presence of homozygous colored males might 

 very easily escape notice unless sufficient numbers of young from 

 a critical cross were raised. It should further be noted that no 

 Sterility is expected nor has any been recorded. 



If a similar change occurred at rare intervals in certain whit- 

 females as we have a right to expect it possibly would, we should 

 have no phamtupiralJi/ ahn-rant or unexpected color classes 

 formed 1 in crosses between such females and colored males. We 

 should however, obtain infrequently as a result of this process 

 homozygous instead of heterozygous.colored males and peculiarly 

 constituted colored females as follows : 



pected: (1) WwFFMM = ,-olnre,l males / commonlr 



(2) WwFFMm = colored females J 



(3) WWFFMM = colored males j 



(4) WWFFMm= colored females} excep lona y * 



only careful individual breeding tests would be ex- 

 veal the presence of the exceptional homozygous 



