THE LAW OF DOMINANCE 339 



character yielded offspring all resembling the dominant parent 

 as regards the character in question. Let us for shortness 

 call the parents D and R, and the first result may be expressed 

 thus : D x R == D. 



It must be carefully noted that the complete dominance 

 which Mendel observed has been shown in other cases to be 

 the exception rather than the rule. Thus a cross between a 

 " Chinese " primula with wavy crenated petals and a " star " 

 primula with flat simply notched petals is intermediate between 

 the two parents ; and yet, as the next generation shows, the 

 case is one of Mendelian inheritance. 



In many cases the hybrid, while on the whole dominant, may 

 show some influence of the recessive character, but not nearly 

 enough to warrant us in speaking of a blend. JThus, when white 

 (dominant) Leghorn poultry are crossed with brown (recessive) 

 Leghorn, most of the offspring have some " ticks " of colour. 

 When these are inbred they produce a quarter brown (extracted 

 recessives) and three-quarters pure white or white with a few 

 ticks. The dominance is not quite perfect. 



The Law of Splitting or Segregation. In the next generation 

 the cross-bred plants (products of D and R, or R and D, but 

 all apparently like D) were allowed to fertilise themselves, with 

 the result that their offspring exhibited the two original forms, 

 on the average three dominants to one recessive. Out of 1,064 

 plants, 787 were tall, 277 were dwarfs. 



When these recessive dwarfs were allowed to fertilise them- 

 selves they gave rise to recessives only, for any number of genera- 

 tions. The recessive character bred true. 



When the dominants, on the other hand, were allowed to 

 fertilise themselves, one-third of them produced "pure" domi- 

 nants, which in subsequent generations gave rise to dominants 

 only ; and two-thirds of them produced once again the 

 characteristic mixture of dominants and recessives in the 

 proportion of 3 : I. 



