FEATHER PIGMENTATION AND INTENSITY 7 



Table 7. — Mean Age at First Egg, Mean Winter Clutch, Mean Winter 

 Production, and Mean Annual Production in Two Lines Through Four 



Generations. 



GENETIC RELATION OF WINTER INTENSITY AND 

 RHODE ISLAND RED COLOR 



Since exhibition Rhode Island Reds are slower maturing than production- 

 bred birds, it is possible that sexual maturity checks the intensification of pig- 

 ment. The difficulty of measuring such a physiological effect is apparent, how- 

 ever. There is also evidence that early sexual maturity does not always prevent 

 the development of the deep shade of pigment desired. The genetically late- 

 maturing birds in the light group showed even a smaller mean clutch size than 

 the late-maturing birds in the dark group. The mmiber of birds concerned in both 

 lines, however, is small. 



The eight smutty birds in the original foundation had a mean clutch size of 

 3.1 which does not indicate that gene E, responsible for smut in under-color, is 

 linked with gene I for medium clutch size. 



Extreme clutch sizes of four or more were equally numerous in both the 

 light and the dark lines of the foundation stock. 



Since the population used carried but a very small proportion of genetically 

 late-maturing birds, it is not possible to adequately study the relation of surface 

 color to late sexual maturity. A group of 31 exhibition pullets hatched and 

 reared in 1929 consisted of 30 genetically late and 1 genetically early. The single 

 early individual had a clutch size of 2.4 and there were three birds in the late 

 group with clutch sizes equal to or greater than this. The mean winter clutch 

 size of the 30 late-maturing birds was 1.4. These data suggest that deeply colored 

 birds are likely to be deficient in winter clutc^h size. 



In general, the data obtained in this experiment show that large clutch 

 size is a little less connnon in the dark birds but that the birds with medium 

 shades of red average high in clutch size in both the light and the dark lines. 

 It seems probable, therefore, that the genetic make-up necessary for very dark 

 plumage color is such that a long developmental period previous to sexual ma- 

 turity is necessary. Since early sexual maturity is rather intimately correlated 

 with large winter clutch size, a large proportion of deeply colored birds might 

 be expected to exhibit low intensity. In view of this fact, it would seem to be a 

 laborious process to establish uniform deep pigmentation and high intensity in 

 a flock, but a medium shade of red should be maintained without difficulty. 

 Care should be taken to select as breeders only birds homozygous for gene B 

 and at the same time showing a winter clutch mean of three or more. 



