INHERITANCE—IMPROVEMENT BY BREEDING 1S1 



recessive (H 135), and that the same applies to the ovules, chap. 

 The chances are therefore equal that if the heterozygote V ' 

 is self-pollinated, as much pollen containing the dominant 

 character will fall on "dominant" silks as pollen contain- 

 ing the recessive character falls on "recessive" silks, the 

 result being progeny homozygous for the dominant and for 

 the recessive characters respectively. But there is equal pro- 

 bability that some pollen with the dominant character will 

 fertilize ovules bearing the recessive character, and vice versa, 

 the net result being the same in either case, i.e., the production 



Black. 



White. 





Pj Zygotes 



- First parental generation. 



□) (□) Pj Gametes' 



Fi Zygote 



E: Sj' 



I heterozygous, Zygo'tes. 



I but black because 

 [black is dominant. 



□> 



(BHl! 



<0§ 





□> 



produces 



produces 



produces 



produces 



homozygous black. 



I heterozygous, but black 

 I because black is dominant. 



(heterozygous, but black 

 I because black is dominant. 



homozygous white. 



Fig. 79. — Diagram to illustrate segregation of characters. 



of a new heterozygote. Thus the chances are equal whether 

 the progeny will be heterozygous or homozygous. In practice 

 we find that about 50 per cent of the progeny of a heterozygote 

 are also heterozygous (if the total number is sufficiently large) ; 

 the other 50 per cent are homozygous, one half of them being 

 like the dominant grandparent and the other half like the 

 recessive grandparent. But as all the heterozygotes contain 

 the factor which is dominant, and as the essential feature of 

 dominance is that it masks the presence of the recessive, we 



