258 T. H. MORGAN. 



bers obtained are in fair agreement with this expectation. If 

 two factors are necessary for hen-feathering, the back-cross ex- 

 pectation would be 4 hen-feathered to 12 cock-feathered birds, 

 which differs so much from the results obtained that the assump- 

 tion of a single factor-pair seems the more probable. 



In former years I have obtained 127 F 2 offspring from the 

 above cross of Sebright by Game Bantam and its reciprocal. 

 These have been recorded in the Carnegie paper (Table I., page 

 19). There were 55 males in the records. If a single pair of 

 not-sex-linked genes was involved in the cross, the expectation in 

 F 2 would be, three cock-feathered males to one hen-feathered 

 one. If two pairs of genes were involved either one of which is 

 sufficient for the development of hen-feathering the expectation 

 in F 2 would be 9 to 7; if both are necessary the expectation is 15 

 to i. There were 29 hen-feathered, and 26 cock-feathered birds. 

 It was pointed out that these data seem in better agreement with 

 a two-factor pair, than with a one-factor pair assumption. But, 

 as pointed out above, the old and the new data combined for the 

 back-cross, appear to fit better the single factor pair assumption. 



There is one other possibility that may be considered. If 

 there is one dominant factor, D 1 , for hen-feathering in the' Se- 

 bright, and a modifier that intensifies the action of D 1 , but alone 

 or in duplex does not produce hen-feathering, the expectation 

 for Fo is 12 to 4, and for the back-cross I to I. The former ratio, 

 which is of course the 3 to I, does not fit the case any better than 

 one factor alone, although it might help to explain the inter- 

 mediate type o>f male, as due to the presence of a normal allelo- 

 morph of the intensifier. 



Color Inheritance in the Cross of Sebright to Game. 



It is now possible to add a few more cases to the data for color- 

 inheritance. Four back -cross hens were reared (1919), that fall 

 in the former classes (Carnegie Publication, No. 285, pages 

 19-20) B, G, A, A. One of the four is almost exactly like the 

 game-hen. The cockerels fall into the classes, B, G (or H}, S, 

 S, S, K, E. 



Of these n back-cross birds two were almost exactly like the 

 game (one female, one male). For two pairs of color factors, 



