n8 



MENDELISM 



CHAP. 



stitution of the F l is a ffPpli, and such a bird 

 produces in equal numbers the four sorts of gametes 

 fPf, fPi, fpl, fpi. The constitution of the F l ? in 

 this case is FfPpIi. Owing to the repulsion between 

 F and / she produces the four kinds of gametes 

 FPi, Fpi, fPI, fpi, and produces them in equal 



numbers. The 

 result of bringing 

 two such series of 

 gametes together 

 is shown in Fig. 

 28. Out of the 

 sixteen types of 

 zygote formed one 

 (FfPPit) is homo- 

 zygous for the pig- 

 mentation factor, 

 and does not con- 

 tain the inhibitor 

 factor. Such a 

 bird is as deeply 



pure Silky parent. 

 Two, again, contain a single dose of P in the absence 

 of /. These are nearly as dark as the pure Silky. 

 Four zygotes are destitute of P though they may or 

 may not contain /. These birds are completely devoid 

 of pigment like the Brown Leghorn. The remaining 

 nine zygotes show various combinations of the two 

 factors P and /, being either PPIi, PPII, PpII, or 

 Ppli, and in each of these cases the pigment is more 

 or less intense according to the constitution of the 

 bird. Thus a bird of the constitution PPIi 



FIG. 28. 



r 



Diagram to illustrate the nature and composition of 

 the F 2 generations arising from the cross of Silky 

 hen with Brown Leghorn cock. 



