176 GENETICS 



6. BLENDING INHERITANCE 



In the instances of imperfect dominance given above, 

 where the progeny of unlike parents present an inter- 

 mediate condition, it is found that, upon cross-breed- 

 ing 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 re- 

 sults, on a scale in which ten represents complete boot- 

 ing, and zero, no booting or clean shank (Davenport). 

 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-important factor is segre- 

 gation. 



Are there, then, any cases where true fusion of 

 hereditary parental traits occurs, in other words, 

 where segregation in the second filial generation does 

 not appear? Does the "melting-pot of cross-breed- 

 ing" ever "melt" the characters thrown into it? 



It was formerly believed that diverse parents gener- 

 ally produce intermediate offspring, and that this 

 intermediate condition continues without any segrega- 

 tion at all in the form of "blending inheritance," but 

 within the last decade apparent cases of blending in- 

 heritance have been thrown out of court one after the 

 other by the Mendelians. Bateson, in an inaugural 



