282 Genetic Studies in Poultry 



is from 6 — 11. Those belonging to the more deeply tinted group are 

 about thrice as numerous as the white and faintly tinted ones. 



These are the chief facts with regard to egg-colour that have come 

 from our researches, and before passing on to some special points we 

 may consider their possible orientation. The data are clearly insufficient 

 to justify any attempt at precise factorial analysis. Such analysis as 

 we can pretend to must obviously be rough, and our only excuse for 

 making it is that it may perhaps offer hints for future work to others. 



We suggest then that the cases of the Langshan $ x Brown Leg- 

 horn cT (Fig. 2) and of the Langshan % x Hamburgh (/• (Fig. 3) are on 

 the same plane, and may be taken together (Fig. 4) — that we are 



*l 



1234 56789 10 11 

 Fig. 4. In this figure the data given in Figs. 2 and 8 are combined. 



concerned here with a principal factor leading to increased tint of egg — 

 that this factor is present in a homozygous state in the Langshan, but 

 absent from the Hamburgh and the Brown Leghorn — that in the 

 heterozygous state the tint is intermediate. Further we suggest that 

 the egg tint is also dependent upon one or more minor factors, which 

 are present in the Langshan but not in the Hamburgh or the Leghorn. 

 The effect of their presence is to lead to tinted shell, but only to a minor 

 degree. The really dark egg must owe its colour to the principal factor, 

 but the colour will be deeper if the minor factors are also present. 



Our suggestion may perhaps be made clearer if we attempt to 

 illustrate it by a concrete example. Let us suppose the dark egg breed 

 to be homozygous for a major, and for one or more minor factors, while 

 the white egg breed with which it was crossed contains none of these 

 factors. If the various factors are inherited alike by either sex the 

 distribution of egg-colour in the F^ generation will be not unlike the 

 scheme shown in Fig. 5. One-quarter of the F2 birds will lack the major 

 factor, and their eggs may be supposed to range between grades 1 — 4 

 according to their constitution with regard to the minor factors. The 



