THEORY OF REVERSION 221 



The puiple-spot appears in the zygote produced 

 because the factor for grey-coat and purple-spot 

 co-exist in this zygote. The reason of its absence from 

 either parent will be seen from their zygotic formulae ; 

 the grey-coated is GGpp, i.e. grey but no purple- 

 spot ; the white is ggPP, i.e. purple-spot but no grey. 

 Germ-cells of four kinds, according to the character- 

 factors which they contain, would be produced by 

 the hybrid, namely GP, Gp, gP, gp, and the number 

 and kinds of zygotes produced by their random union 

 can be discovered, as in the case of the 9:3:3:1 

 ratio, by plotting their possible combinations on a 

 sixteen-square Table. This Table conforms precisely 

 to the general type given on p. 214. 



cJ gametes 

 GP Gp gP 



gp 



GP 



Ol- 



Gp 



gP 



gp 



