DOCTRINE OF EVOLUTION AND RELATED IDEAS 



491 



they bred true dwarf indefinitely. Close-breeding the tails 

 showed them to be of two kinds: (i) one- third of them (that is, 

 one-fourth of the whole offspring) were just as pure as the dwarfs 

 were, and continued to produce tall forms indefinitely. Two- 

 thirds of the tails (one-half the total offspring) when inbred 

 had three tall offspring to one dwarf, just as had been true of the 

 first hybrid generation. Further inbreeding of the hybrid off- 

 spring continues to repeat these proportions indefinitely:-! 12:1, 

 that is one pure tall, two hybrid tails, and one pure dwarf. 



FIG. 253. 



C X c Parental Generation 



C(c) ist Filial Generation 

 (Self-crossed) 



FIG. 253. A general formula for Mendelian crosses. C represents any dominant quality; 

 c, the absence of the quality, or the recessive. The first filial generation are all hybrids that look 

 like the dominant parent. If these are self-bred, the offspring of the second filial generation, F, 

 will be one-fourth pure dominant (C), one-fourth pure recessive (c}, and one-half hybrids which look 

 and breed like their hybrid parents. CC and C(c) look alike, but breed differently. Compare 

 with Fig. 252. 



Mendel also found that yellowness of seed coat was dominant 

 over greenness; that smoothness of seed was dominant and 

 wrinkledness was recessive. He also found that these different 

 qualities were inherited absolutely separately; that is to say 

 that the yellow or green and the smooth or wrinkled quality 

 of the seeds might be transmitted equally in connection with 

 either the dwarf or the tall. 



The results stated in general terms might be expressed as 

 follows : When pure bred parents differ by the presence or ab- 

 sence of a certain heritable quality, all the offspring of the first 

 generation will be like one of the parents in bodily appearance. 



