192 Bulletin No. 155.— 1913. 



divided between the sexes ; 2 of the three barred birds should be cf cf 

 and all black birds should be 99; moreover, one of the barred 

 males should be homozygous for the barring factor while the other 

 cT" and the 9 should be heterozygous. Other birds both d^ and 9 

 carry the barring factor but do not visibly manifest the barred pattern 

 because they are either homozygous or heterozygous for I, — a cir- 

 cumstance which prevents the appearance of the pigment and there- 

 fore of the barring also. 



Having thus outhned the expected results in the Fo generation 

 from White X Black crosses, provided the White Leghorn d^ was 

 actually homozygous for barring and actually possessed the in- 

 hibiting factor /, we may now attempt to ascertain to what extent 

 these theoretical results agree ^vith the experimental data and 

 furnish an interpretation for them. 



Case la. — White Leghorn X Black Hamburg, Fo. — (Tables 3 and 4, 

 pp. 167 and 168). First of all it is apparent that the ratio 3 white: 

 one dark is closely reaUzed among the 117 birds included in Table 

 3 and in the 137 birds comprising Table 4. In the 1911 series 

 (Table 3) the actual results were 90 white : 27 dark, and the expected 

 results 88 : 29. Whereas we should expect only 7 + blacks (all 

 females) we actually have 12 (16 including the grays), including 9 

 99 and 3 in which the sex was not ascertained. In explanation of 

 this discrepancy it may be said that in young chicks under 2 weeks 

 of age, it is difficult to distinguish accurately the blacks from the 

 barred. In case chicks die during the first week or two, all those 

 which might later develop barring must be described as black. 

 There can therefore be no doubt that several of the birds described 

 as black would have become barred if they had lived. The only way 

 seen at present to avoid this difficulty is to embod}' in the tables no 

 chicks which die when less than 3 weeks of age. This plan was 

 adhered to in the formulation of Table 4. 



Regarding the barred birds, it is clear that more are called for 

 (21-|-) than actually appeared (11); but as already explained, the 

 •deficiency would probably have been made up by addition of the 



