22 MASS. EXPERIMENT STATION BULLETIN 396 



Mortality rates were low in both groups, but the data are not adequate to show 

 differences. 



A comparison of the + and — groups with respect to back feathering at 8 

 weeks shows the two groups to be very similar in body weight. In mortality 

 rate the + group was somewhat lower than the — group, although the rates 

 were low in both classes. 



Table 10. — Relation of Chick Feathering to Body Weight and 

 Mortality Rate in Males. 1934 - 1941. 



Number Body Number Mortality 



Feathering Class of Weight at of Rate to 



Birds 5 Months Birds 5 Months 

 Pounds Percent 



Chick feathering at 12 days 



Rapid (slsl) 



Slow (SI) 



Back feathering at 8 weeks 



Feathered ( +) 



Bare (-) 



The data in table 10 do not in general indicate superior growth in rapid feather- 

 ing cockerels up to 5 months of age. There is some evidence, however, to indicate 

 a lower mortality rate in the rapid feathering groups. 



Special Results of Matings in 1942 



In addition to the regular complement of females from line 1, three females 

 from line 2 were mated to the line 1 sire to study the inheritance of the sex-linked 

 gene si and other genes affecting degree of back feathering. In these matings 

 each bird was classified for the recessive sex-linked gene si by the presence or 

 absence of tail growth at 12 days. All individuals were also graded for degree 

 of back feathering at 8 weeks of age into grades 0, 1,2, 3, and 4. For example, 

 slsl 4 means that the male had a tail when 12 days old and also had complete 

 back feathering at 8 weeks of age. 



The first mating of the slsl 4 male and a si 3 female gave only slsl 3 sons and 

 daughters. A second mating of the slsl 4 male to a SI 1 female gave 2 SI sons, 

 3 SI 1 sons, 9 SI 2 sons, and 4 SI 3 sons. This is a ratio of 12 intermediate 

 (grades 1 and 2) to 4 grade 3 to 2 grade 0. It seems probable that the sire was 

 slslXx in genetic makeup and that the dam was SlXx. Such a mating should 

 give all male progeny heterozygous for gene si, of which 25 percent should be 

 SIslXX, 50 percent SlslXx, and 25 percent Slslxx. The actual proportions were 

 4-12-2. The 11 daughters were all placed in grade 3 (si 3). A third mating was 

 made between the slsl 4 male and a SI 2 female. This mating gave 14 sons, all 

 heterozygous for gene si. In back feathering there were 3 grade 3, 10 inter- 

 mediate, and 1 grade 0. The expectation was 1-2-1 or 4 2/3 to 7 to 4 2/3. From 

 this last mating there were 9 grade 3 daughters and 1 of grade 2, all carrying 

 recessive gene si. 



A cross was also made between line 1 and line 2, using an si 3 dam from line 

 1 mated to the line 2 sire which was SlSl in makeup. This sire was homozy- 

 gous for gene SI and gave 13 sons, all graded SI 2. The 19 daughters were also all 

 graded as SI 2. As was to be expected on the basis of a smgle autosomal factor, 

 all sons and daughters were intermediate in back feathering. All 32 progeny failed 

 to exhibit the recessive sex-linked gene for rapid feathering. 



