26 THE GENETIC AND THE OPERATIVE EVIDENCE 



F2 results. Thus, in the cross of Silky to Minorca, that gives black 

 Fi birds, the Fj count gave 210 black, 57 game, and 95 white — ^approxi- 

 mately the expectation for two pairs of factors, one of them giving 

 white (9:3:4). Silky by White Leghorn gave white Fi's, but the males 

 developed red on the wing bow and saddle when they became mature, 

 and the female a faint blush of salmon ("red") on the breast. In F2 

 there were whites, games, and blacks, approximating to expectation for 

 three pairs of factors, one being a dominant white (52: 9: 3). Silky 

 by Buff Cochin gave a washed-out buff, but with the jungle coloration 

 partly developed in the tail (black) and hackles and wing bow (redder 

 buff). Davenport represents the Buff Cochin as having lost the jungle 

 patterns and coloration, while the Silky retains it. The heterozygous 

 condition of the genes for the wild-type color in Fi is made responsible 

 for the part development of color. The White Silky is represented as 

 canying the factor for black (N), hence in F2 both black and game- 

 colored birds are expected and they were obtained. When Black 

 Cochin is crossed to Buff Cochin, the Fi males are in general like the 

 game (black and red) while the females are black (except for some red 

 on the hackle). In this case Davenport represents the Black Cochin as 

 showing a factor for jungle-fowl pattern, but lacking the color that is 

 assumed in his other formulae to go with this pattern. What is meant 

 by this change is not quite clear to me, unless Davenport supposes there 

 is an independent factor for the jungle-fowl pattern which may be 

 filled in by other colors determined by other factors. But were there 

 enough Fi birds to exclude the possibiUty that jungle-fowl birds would 

 not appear in this cross? 



Davenport has reported a cross between a female White Cochin and 

 a male Tosa (wild type) from which the daughters were Tosa, except 

 that the shafting was broadened, and the saddle feathers and proximal 

 secondaries were obscurely barred (black and buff) ; the sons were also 

 like the Tosa, but every feather was repeatedly barred (see above). 

 In F2 there were 15 white, 25 game, and 16 barred birds. Davenport 

 concludes that "barring is clearly heterozygous and confined to the 

 male sex," and in a footnote he adds that the sex-linked barring factor 

 of the Plymouth Rock is different from that of this Cochin-Tosa cross, 

 but Goodale informs me that the barring that appeared in this cross 

 is probably the same as that in Barred Rocks. 



As pointed out, an interesting feature of color inheritance in poultry 

 is the large number of cases of sex-linked inheritance. It might seem 

 probable here, as in the case of Drosophila, that this is due to a well- 

 recognized difference between sex-Unked and autosomal characters, 

 namely, that a recessive mutation in one of the sex chromosomes of a 

 sperm-cell of the male bird will have a chance of showing its effect 

 immediately if that sperm-cell unites with an egg without a Z to form 

 a daughter, whereas it would not immediately show up in the offspring 



