Constitution of the White Leghorn Breed. 159 



barred birds. This result approximates very closely the expected 

 Fi Mendelian ratio.* Since the birds that are heterozygous for white 

 and black appear white, we have 75 per cent, of white birds. Appar- 

 ently Davenport was not working with the pure-bred White Leghorn 

 stock. 



In a cross between White Leghorn and Black Cochin there appeared 

 among 24 offspring, 10 white, 7 black and 7 barred. In this case 

 Davenport assumes that the Leghorn was heterozygous for white 

 (since half the progeny were not white) and heterozygous for barring. 

 Subsequently the barred birds which resulted from the above cross, 

 were mated together. This cross gave 23 white birds, 40 blacks or 

 games, and 21 spangled, barred or blue. Regarding this result 

 Davenport says: '^On the assumption that the zygotic formula of 

 both hens and cocks is BbN2Ww (compatible with barred plumage) , 

 we get four-sixteenths of the offspring white, three-sixteenths mottled 

 or barred, and nine-sixteenths black or game, thus approximating^ 

 the observed result; i. e., 21, 16, 47, as compared with 23, 21, 40. The 

 result supports the hypothesis of a barring factor, B." 



That Davenport obtained barred birds in a cross between White 

 Leghorn Bantam and Dark Brahma has already been mentioned : Of 

 51 Fi birds, 5 were barred. An attempt was made to fix the barring. 

 The best cock bred from F2 and the best females from Fi or F2 were 

 used for the experiment. From this cross there were obtained 3 

 whites, 67 blacks, 37 of Dark Brahma type and 38 barred birds. 

 "This result," says Davenport, ''suggests the interpretation that one 

 of the parents, probably the male, contains both heterozygous black 

 and barring, while the other parent lacks the supermelanic coat and 

 has homozygous barring. Then, of the offspring, half will be barred 

 and half will be black, and consequently (since only the non-black 

 show their barring), one-fourth will appear barred, one-fourth will 

 appear of the Dark Brahma type and half will be pure black, or have 

 the pattern obscured by the supermelanic coat." 



Besides the studies on barring reported above, dealing chiefly with 

 crosses between light and dark birds, the barring of the Plymouth 



*Provided that the White Leghorns were heterozygous for white. 



