94 INHERITANCE OF CHARACTERISTICS IN DOMESTIC FOWL. 







E. THE LIMITS OF SELECTION. 



In the last few decades the view has been widespread that characters 

 can be built up from perhaps nothing at all by selecting in each genera- 

 tion the merely quantitative variation that goes farthest in the desired 

 direction. I have made two tests of this view, using the plumage color of 

 poultry. 



(1) Increasing the red in the Dark Brahma X Minorca cross. The Dark 

 Brahma* belongs to the group of poultry that contains a majority of char- 

 acters derived from the Aseel type. Nevertheless, its plumage is closely 

 related to that of the Jungle-fowl, from which it may be derived on the 

 assumption that the red part of the pattern has become, for the most part, 

 white. However, a little red remains on the middle of the upper feathers 

 of the wing-bar. I crossed such a bird with a Black Minorca, and, as reported 

 in my earlier work,t the offspring were all black, except that the males 

 showed some red on the wing-bar. The amount of red varied in the different 

 males, and I decided to test the possibility of much increasing the amount 

 of the red by selection in successive generations. So I chose the reddest 

 cock to head the pen. In this pen (No. 632) 222 chicks were produced and 

 grew to a stage in wliich their adult color could be determined. Of these 

 222 chiclvs, 160, or 72 per cent, were black, without red; 24, or 10.8 per cent, 

 were black with some red; 38, or 11.7 per cent, were typical Dark Brahmas, 

 and 9 others, or 4.5 per cent, were modified Dark Brahmas. 



The following year (pen 732) I bred a cock derived from the last year's 

 pen, a bird that resembled much the male Dark Brahma (except that it 

 was somewhat darker), to sundry hens, hybrids between the Dark Brahma 

 and Minorca some of the first and some of a later hybrid generation, but 

 all black except that some of the 1906 birds had a little buff on the breast 

 and the primaries. The F, (black) XF^ (Dark Brahma) gave 51 per cent 

 black offspring, 27 per cent with a black-and-red Game pattern, and 22 per 

 cent with the Dark Brahma pattern devoid of red. Thus the third genera- 

 tion suddenly gave me a red-and-black Game-colored bird (plate 12) ! 



My interpretation of the foregoing results is as follows: The Dark 

 Brahma gametic formula proves to be CIrnwx, whereas the Black Minorca 

 is C{IR)Ntvx, where {IR) is equivalent to, and merely a further analysis of, 

 the J of the formula of the Minorca as given in earher sections. The / 

 stands for the Jungle pattern without red and R is the red element in that 

 pattern. Obviously A^ and R are the differential factors, 4 kinds of gametes 

 occur in Fj, and in every 16 offspring these factors are combined in the 

 following proportions : 9 NR, 3 Nr, 3 nR, 1 nr (compare the distribution of 

 color types in the 222 offspring of pen 632) . The F^ male selected as father 

 of the next generation (in pen 732) was an extracted Dark Brahma in 

 coloration and probably formed only 1 kind of gamete, nr; but the hens 



Plate 11. t Davenport, 1906, page 35. 



