W. Bateson and E. C. Punnbtt 199 



at all should be deeply pigmented. On the other hand all the male 

 gametes of the F^ $ which contain P contain also I, and consequently 

 none of the pigmented (/(/ produced should be deeply pigmented. 

 Table XI which gives the details of four such experiments shows how 

 closely this expectation is realised, and offers strong corroborative 

 evidence of the view here taken of the nature of the gametes produced 

 by this type of i^i % . The five exceptions recorded we shall refer to 

 again (p. 200). 



The Constitution of the Brown Leghorn Hen. 



While the Brown Leghorn j/" is homozygous for the inhibiting factor, 

 the % is on our hypothesis always heterozygous for this factor. And 

 since we assume repulsion to take place during gametogenesis between 

 the factors F and / it follows that she produces two kinds of gamete, 

 viz. Fpi and fpl. The possession of the ppii strain enabled us to 

 devise a pretty experiment to test this view. By mating a Brown 

 Leghorn ^ with a cock of the constitution jfj3/)M we obtained a number 

 of unpigmented chickens of both sexes. On our hypothesis only the 

 {/'(/' should receive the inhibiting factor, being in constitution ffppli, 

 while the % % should be Ffppii, and consequently lacking the inhibiting 

 factor. This difference between the sexes with regard to the inhibiting 

 factor should be brought out by a cross with fully pigmented homozygous 

 birds (PPii), for while the females should give only fully pigmented 

 chicks, the males may be expected to produce fully pigmented and 

 partially pigmented chicks of both sexes in equal numbers. During 

 the present year a cockerel (ex Br. Leg. ? x ppii J") was mated with 

 a pure Silky hen, and four sister pullets were put with an F2 fully 

 pigmented (/ (No. 40, ex Pen 15, 283 of 1907) already shown to be 

 PPii in constitution. The results are shown in Table XII and are in 

 accordance with expectation. 



TABLE XII. 



Reference Nature of mating &^ w zi '■^ oi 'A 



1910 Pen 8, 150 Silky ? x ,J (ex Br. L. ? x ppii <f ) 1 4 — 3 3 — 



,, 24, 4? 2 ? ?(exBr. L. ? xppiii)x i PPii 18 — — 26 — — 



