12 MASS. EXPERIMENT STATION BULLETIN 316 



males, also a greater tendency for smut to occur in females with the lighter 

 shades of plumage color. 



In general, the study of the exhibition stock showed that smut was more com- 

 mon in the male sex. When exhibition stock was crossed with production stock, 

 observation of the progeny from eight different types of matings showed that, 

 when smut appeared in birds with light surface color, it was more likely to be 

 in the females. Possible sex-linked inheritance of smut is therefore suggested, 

 but the tendency for the smut character to be more prevalent in the male sex 

 regardless of surface color persisted in the different crosses. There was some 

 evidence that smut is associated with dark surface color. 



Under Color and Smut 



Smut may be so extensive in the under color as to almost completely displace 

 the normal red color. On the other hand, smut may be confined to a very narrow 

 band in the feather fluff and may be observed only in certain body regions. Be- 

 tween these two extremes there are many gradations. As a rule, smut in under 

 color is most likely to occur in the back; consequently all birds in these studies 

 were carefully examined in the back region between the points of attachment 

 of the wings. No attempt was made to record the different degrees of smut- 

 tiness. Under color was grouped into four shades of red. The relation between 

 smut and under color in the exhibition stock and in the hybrid progeny is sum- 

 marized in Table 6. 



In the exhibition stock the under color was essentially the same for the smutty 

 and the non-smutty groups of males. Among the females, however, there were 

 more than three times as many non-smutty as smutty, and the great majority 

 of non-smutty females showed dark under color. There is also some evidence 

 in the females that smut in under color may lighten the shade of red pigment in 

 the feather fluff. 



In class 1 of the Fi generation, medium and dark under color were more prev- 

 alent in non-smutty individuals in both sexes. There was still a greater propor- 

 tion of females than males with dark under color and no smut. Furthermore 

 there was evidence of blending in shade of under color in both sexes. 



The greater percentage of non-smutty progeny in class 2, when production 

 males were used, suggests sex-linked relations for the transmission of smut. 

 The fact that all males showing dark under color were free from smut indicates 

 that smut is not a necessary accompaniment of dark red under color. 



The F2 offspring of both sexes averaged intermediate in under color, while 

 42 per cent of the males and 38 per cent of the females showed smut. The 

 original exhibition stock showed 48 per cent of males with smut and 23 per cent 

 of females. The combined Fi generation gave 30 per cent of the males and 

 36 per cent of the females with smut. The gross data suggest that smut segre- 

 gated as a dominant in the F? generation. Dark under color was prevalent in 

 F2 birds of both sexes that were free from smut. 



The limited data for class 4 indicate that smut is rather commonly associated 

 with light under color in females. In the male progeny this relation does not 

 hold, in these hybrids at least. 



Progeny from the back cross, class 5, are rather similar to those in class 4. 

 The data do not indicate, however, that light under color and smut are more 



