i6o 



MENDELISM 



CHAP. 



stitulion of the F^ ^^ is a ffPpIi^ and such a bird 

 produces in equal numbers the four sorts of gametes 

 fPI, fPiyfpI, fpi. The constitution of the F^ $ in 

 this case is FfPpIi. Owing to the repulsion between 

 F and / she produces the four kinds of gametes 

 FPiy Fpi, fPI, fply and produces them in equal 



numbers. The 

 result of bringing 

 two such series of 

 gametes together 

 is shown in Fig. 

 45. Out of the 

 sixteen t\'pes of 

 zygote formed, one 

 {FfPPiz) is homo- 

 zygous for the pig- 

 mentation factor 

 and does not con- 

 tain the inhibitor 

 factor. Such a 

 bird is as deeply 



Fig. 45. 



Diagram to illustrate the nature and composition of 



the F2 generations arising from the cross of Silky picrmented aS thc 

 hen with Brown Leghorn cock. ^ ^ 



pure Silky parent. 

 Two, again, contain a single dose oi 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 remain- 

 ing 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 



