A FURTHER STUDY OF SIZE INHERITANCE IN 



DUCKS WITH OBSERVATIONS ON THE 



SEX RATIO OF HYBRID BIRDS 



JOHN C. PHILLIPS 



Laboratory of Genetics of the Bussey Institution 



SEVEN CHARTS 



In a previous number of this journal the writer reported the 

 result of a cross between two races of ducks differing in size. The 

 number of offspring produced was small, but tended to show a 

 marked increase of variability in size in F2. 



In the breeding season of 1912 more data were obtained from 

 the same stocks, 57 Fi and 31 F2 ducks being raised to maturity. 

 Growth curves were made for all these ducks from an early age 

 until such time as they were considered adult, or nearly so. The 

 average length of this period is 142 days. The growth curves 

 give a good check on the adult or autumn weight of the individ- 

 ual, and enable one to assign the proper weight figure to each bird 

 with very fair precision. The ducks were weighed at intervals 

 of one week to two weeks. 



The curves will be considered later on, together with the growth 

 rate of a race of pure wild mallards reared in 1912. 



As a further test of the parent stocks, which it may be recalled 

 consisted respectively of Rouen ducks and domesticated mallards 

 of a particular strain, 9 pure Rouen and 20 mallards were reared 

 in 1912. The weight of these animals at five months of age is 

 recorded in table 8. 



To produce another lot of Fi ducks, one of the original Rouen 

 males was mated with three female mallards taken at random 

 from among the same birds used in the previous work. For the 

 F2 generation, the same three Fi females as had been used the 

 previous year, Nos. 83, 101, and 106, were mated with Fi male 



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