10 MASS. EXPERIMENT STATION BULLETIN 316 



In class 6 progeny, all birds with standard surface color carried either dark or 

 medium under color. This group of birds showed decidedly darker surface and 

 under color than the class 5 progeny. About 95 per cent of the birds from the 

 exhibition males carried either medium or dark under color compared with about 

 51 per cent of those from the production males. 



The number of birds concerned in class 7 is inadequate to furnish much infor- 

 mation regarding surface and under color. The data suggest that males tend to 

 be darker in under color than females when the dams carry dark color and the 

 sires lack it. 



The progeny of exhibition males X F2 females were all medium or dark in 

 under color. Surface color was also largely dark or standard. There is also some 

 evidence that males showed darker under color than females. This fact would 

 lend support to the idea that some sex-linked genes are concerned in under color. 



In general, a study of the relation of surface and under color in various crosses 

 of Rhode Island Reds indicates that dark surface and dark under color show 

 considerable association. There is also evidence that light modifiers for under 

 color are dominant to dark modifiers. Some evidence is also available which 

 indicates sex-linked inheritance for at least part of the under color modifiers. 



Surface Color and Smut 



A smutty or slatey coloring in the feather fluff of Rhode Island Reds is an 

 undersirable character. Nevertheless, breeders of exhibition birds find this 

 character not at all uncommon and often use female breeding stock showing 

 some smut for the purpose of improving surface color in the offspring. It is 

 therefore important that consideration be given to the relation of smut and sur- 

 face color in the various types of stock available. Table 5 presents a summary 

 of the relation between surface color and smut in the exhibition stock and hybrid 

 progeny. 



Of the exhibition males of standard surface color, half carried smut in under 

 color and half lacked smut. Of the females with standard color, only about one- 

 fifth carried smut. These same proportions hold regardless of surface color, and 

 suggest that smut is much more prevalent in the male sex. 



Since none of the production birds used for crossing were of standard surface 

 color and very few carried smut, there is opportunity to study the behavior of 

 smut in crosses. 



Of the Fi offspring in class 1, males with either dark or standard surface color 

 carried smut or were free from smut in almost equal numbers. Females with the 

 same surface color showed about 36 per cent with smut. Of the 40 males classed 

 as medium or light in surface color, about 32 per cent carried smut. Of the 41 

 females belonging to the medium or light classes, about 49 per cent showed smut. 

 The Fi generation as a whole was made up of 27 smutty males to 43 not smutty 

 and of 24 smutty females to 28 not smutty. There was, therefore, a greater 

 proportion of smutty individuals in the female progeny, suggesting that sex 

 linkage may play a part in the transmission of smut. 



The Fi progeny in class 2 were distinctly lighter in surface color and freer 

 from smut than the Fi progeny from the reciprocal cross (class 1). Only 10 per 

 cent of the male progeny from production males carried smut and 24 per cent of 

 the females, while 39 per cent of the Fi males and 46 per cent of the Fi females 



