47$ 



GENETICS IN DELATION TO AGRICULTURE 



dicate that the character differences depend upon single factor differences. 

 As a matter of fact most instances of imperfect dominance are probably 

 due to complex factor interaction, and they, therefore, require further 

 study. The list as it stands is more interesting than useful, but it gives 

 a rather vivid idea of the variety of character contrasts which may be 

 obtained in the barnyard fowl. Aside from a few additions and changes 

 in wording, this list is essentially the same as that compiled by Hadley 

 for the 1915 "American Poultry Yearbook." 



FIG. 191. Results of crossing White Plymouth Rock and White Leghorn. A, Pi eft 

 White Leghorn; C, Pi 9 , White Plymouth Rock; B, Fid 1 , showing a little flecking of black 

 and a barred tail feather; D, Ft 9 , type of barred birds obtained in Ft. (After Hadley.) 



The most important kind of Mendelian work is that which leads to 

 some definite analysis of the factor complex characteristic of a given 

 breed. As an illustration of such investigations we have Hadley's 

 analysis of the genetic constitution of the White Leghorn breed. White 

 is often dominant in fowls, so that white breeds may carry latent color 

 and pattern factors in their makeup. Hadley finds the White Leghorn 

 to be of the genetic constitution CCII(BZ)(BZ), if a male, and CCII 

 (BZ)W, if a female, the factors having the following effects: 



