4 MASS. EXPERIMENT STATION BULLETIN 396 



weeks of age the birds were graded into + and — groups, depending upon the 

 development of some back feathering or the lack of any back feathering. 



A total of 1494 males was examined at 12 days and again at 8 weeks of age. 

 At the same time 1436 females were examined and classified. The summary 

 appears in table 1. 



Table 1.— Chick Feathering at 12 Days and 8 Weeks of Age. 

 Foundation Flock— 1933. 



Males Females 



At 12 Days SI slsl SI si 



At 8 Weeks -+-+ - + - + 



Totals 1275 83 92 44 505 666 63 201 



Of 1494 males examined, only 136 or 9.1 percent carried the sex-linked gene 

 si in homozygous condition, and 92 of these (67.6 percent) failed to develop back 

 feathering at 8 weeks. Out of 1358 males in which there was no tail development 

 at 12 days, 83 had back feathering at 8 weeks. 



In the female population 18.3 percent carried the sex-linked gene si, and 23.8 

 percent of these failed to develop back feathering at 8 weeks. Out of the total 

 of 1172 that lacked tail growth at 12 days, 56.8 percent showed back feathering 

 at 8 weeks. 



Only 127 or 8.5 percent of the males in the foundation stock carried complf te 

 back feathering at 8 weeks, while over 60 percent of the females had complete 

 back covering at 8 weeks. Furthermore, out of 1358 males that were not homo- 

 zygous for gene si, 6.1 percent developed back feathering in comparison with 

 32.4 percent in males carrying recessive gene si. 



Opportunity is given for study of the relations of the gene for early tail growth 

 and genes for back feathering later on in this report. 



Development of Feathers in Different Body Regions 



Observations were made weekly for 8 weeks, on 419 chicks in lines 1 and 2 

 hatched in 1934 and 1935. The feather tracts studied were head, neck, breast, 

 shoulder, back, abdomen, thigh, leg, and. tail. In table 2 the sexes are recorded 

 separately and the mean age when feather growth started and when it was com- 

 pleted is indicated for line 1 , bred for complete back feathering at 8 weeks, and 

 line 2, bred for absence of back feathering at 8 weeks. 



Table 2. — Mean Age in Weeks When Feathering Started and was 

 Completed. 1934 and 1935 — 419 Chicks. 



