K. C. PUNNBTT AND THE LATE MaJOR P. G. BaILEY 283 



other three-quarters will contain the major factor and will vary between 

 grades 5 — 11 according as this major factor is associated with one or 

 more of the minor factors. Moreover the depth of tint may further 

 depend upon whether the bird is homozygous for the major or for the 

 minor factors. In this way we can form a rough interpretation of the 

 nature of the F^ generation such as that shown in Fig. 4. 



123456 789 10 11 



Fig. 5. Ideal scheme of distribution of grades of egg-colonr in F2 . For explanation see text. 



We have already seen however that the F^ curve of egg-colour for 

 the birds ex Brown Leghorn $ x Langshan (/" is of quite a different 

 type (Fig. 1), and is characterised by the enormous preponderance of 

 white and of lightly tinted eggs. Now a curve of such a nature can be 

 readily formed from our ideal curve (Fig. 5) if we suppose that the ^1 

 birds are of similar constitution with regard to the factors leading to 

 pigment production, but at the same time are heterozygous for a factor 

 leading to the inhibition of pigmentation in the eggs. Suppose that this 

 ■ inhibitor turns grades 1 — 6 into grade 1, grade 7 into grade 2, 8 into 3, 

 9 into 4, 10 into 5, and 11 into 6: and suppose further, for the sake of 

 simplicity, that its action is similar whether the bird be homozygous or 

 heterozygous : then our ideal curve shown in Fig, o is transformed into 

 the curve shown in Fig. 6. Without harrying the point too closely it is 

 clear that such a curve bears a fair resemblance to the actual curve met 

 with in Fig. 1. If we accept this interpretation we must suppose that 

 the Boys-Smith strain of Brown Leghorn was homozygous for this postu- 

 lated inhibitor, which was lacking in the purchased Brown Leghorn ^^ 

 and in the Hamburgh. There is the point of course that where the 

 white egg breed was the mother one type of F^ family appeared, and 

 that where it was the father another type appeared: but in the absence 

 of further data it seems hazardous to regard this as anything but a 

 coincidence. 



Though the interpretation which we have suggested is in fair 



accordance with the experimental data so far given, there is one further 



. set of experiments which offer a difficulty to that interpretation. The 



two Fx ^ ^ ex Langshan x Hamburgh were crossed with several 



Hamburgh % %. Since such F^^^ mated with similarly bred F^%% 



20—2 



