286 Genetic Studies in Poultry 



suggest that there is some form of linkage between the factor for black 

 down and that for our postulated inhibitor of egg-colour. But when it 

 is recollected that the inhibitor originally entered the cross from the 

 side opposite to that from which the black entered, it is clear that we 

 cannot be dealing with an ordinary case of linkage. 



B. In the Hamburgh -Langshan cross. 



The down-colour of the Gold Pencilled Hamburgh is pale golden 

 with dark brown spotty markings on the back of the head, and generally 

 also on the body. The down-colour of F^ birds is that of blacks. In 

 the F^ generation four main types of down could be distinguished, viz. 

 black, brown stripe, pale gold (similar to that of the Hamburgh), and 

 chocolate. The last mentioned exhibited considerable variation. The 

 predominant colour was always rich chocolate, but in some cases the 

 chick could be described as a chocolate stripe, while in others the colour 

 was uniformly distributed, and in others again their might be a slight 

 admixture of black. Chick black in down developed into blacks : the 

 pale golds developed into gold barred birds of various sorts : the brown 

 stripes into a miscellaneous lot of browns and gold browns. The choco- 

 lates however gave two distinct classes of plumage, viz. gold barred of 

 various kinds, and blacks, these last always with some brown mossing in 

 the wings or else with some gold in the hackle'. No full black was 

 actually reared from a chocolate chick though this may have been due 

 to paucity of numbers. Of 31 chicks with chocolate downs reared 11 

 developed into blacks. 



Out of the four kinds of down the actual numbers recorded for the 

 several F^ families were 



Blk. Choc. Br. Str. Gold 



96 50 31 16 



But if we reckon one-third of the chocolates as potential black-plumaged 

 birds our ratio for the plumage characters, black as opposed to non- 

 black, becomes 



Black Non-Black 



96 + 17 = 113 33 + 31 + 16 = 80 



This is very close to a 9 : 7 ratio where expectation would be 109 blacks : 

 84 non-blacks. The conclusion that the Hamburgh lacks two factors 

 necessary for black is supported by the results of crossing F^ birds with 

 Hamburghs. 



^ These descriptions refer throughout to the pullets. For reasons of economy the 

 cockerels were killed off at an early stage. 



