272 HEREDITY AND ENVIRONMENT 



neither white nor red flowers but pink ones, 

 and the F 2 plants bear white, red and pink 

 flowers. The whites and reds are always 

 homozygous, the pinks heterozygous; pure 

 white and pure red are produced only when 

 their factors are duplex (WW), (RR) ; when 

 they are simplex ( WR ) pink is produced. In 

 this case red is not completely dominant over 

 white, but the hybrid is more or less interme- 

 diate between the two parents (Fig. 50). 



It has long been known that the race of 

 fowls called Blue Andalusian does not breed 

 true, but in each generation produces a certain 

 number of blacks and whites as well as blues. 

 Bateson found that the blues are really hybrids 

 between blacks and whites in which neither of 

 the latter is completely dominant. Black and 

 white appear only when they are pure (homo- 

 zygous), blue only when both black and white 

 are present (heterozygous). 



Again a cross of red and white cattle pro- 

 duces roan offspring, but the latter when in- 

 terbred give rise to reds, roans and whites in 

 the proportion of 1 :2 :1, showing that the roans 

 are heterozygotes in which red is not com- 



