182 GENETICS 



6. Blending Inheritance 



In the instances of imperfect dominance given 

 above, where the progeny of unhke parents present 

 an intermediate condition, it is found that, upon 

 cross-breeding these offspring, segregation into the 

 grandparental types occurs just as truly as in instances 

 of complete dominance. 



In poultry, for example, when Cochins, which are 

 "booted," and Leghorns, which are clean-shanked, 

 are crossed, booting of an intermediate grade of four 

 results, on a scale in which ten represents complete 

 booting, and zero no booting or clean shank (Daven- 

 port). The character of booting and its alternative 

 absence, however, segregate out in true Mendelian 

 fashion when these hybrids are subsequently crossed 

 together. It is evident that dominance plays only 

 a secondary role in such cases, and that the all-im- 

 portant factor is segregation. 



Are there, then, any cases where true fusion of hered- 

 itary parental traits occurs, in other words, where 

 segregation in the second filial generation does not 

 appear? Does the "melting-pot of cross-breeding" 

 ever "melt" the characters thrown into it .^ 



It was formerly believed that diverse parents 

 generally produce intermediate offspring, and that 

 this intermediate condition continues without any 

 segregation at all in the form of "blending inheritance," 

 but within the last decade apparent cases of blending 

 inheritance have been thrown out of court one after 

 the other by the Mendelians. Bateson, in an inaugural 



