192 GENETICS AND EUGENICS 



Color dominant over albinism. 

 Black dominant over yellow. 

 Short hair dominant over long hair. 



As regards ear-length, neither dominance nor segregation 

 of the difference between the parents is observable. All the 

 Fi as well as the r2 individuals have ears of intermediate 

 length. The inheritance is what has been called blending. 

 The same is true as regards size of the body. 



In Fig. 130 the skulls of the parents are shown with the skull 

 of the Fi individual between them. In absolute dimensions, 

 as well as in the proportions of its parts the Fi skull is strictly 

 intermediate. The same blending effect was observed in all 

 other parts of the skeleton. 



The multiple factor hypothesis. It is clear that in blending 

 inheritance there is no dominance, but the suggestion has 

 been made that nevertheless segregation may occur, and so 

 the inheritance may have a Mendelian basis. This suggestion 

 was first made by a Swedish plant breeder, Nilsson-Ehle 

 (1909) who obtained some very peculiar inheritance ratios in 

 crosses of wheat differing in color of seed or of chaff. 



When a variety having brown chaff is crossed with one 

 which has white chaff, the hybrid plants are regularly brown 

 in Fi and three brown to one white in F2, but a particular 

 variety of brown-chaffed wheat gave a different result. In 

 fifteen different crosses it gave uniformly a close approxima- 

 tion to the ratio 15:1 instead of 3:1. The totals are suffi- 

 ciently large to leave no doubt of this. They are one thou- 

 sand four hundred and ten brown to ninety-four white, 

 exactly 15 :1. This is clearly a dihybrid Mendelian ratio, and 

 Nilsson-Ehle interprets it to mean that there exist in this 

 case two independent factors, each of which is able by itself 

 to produce the brown coloration, though no qualitative 

 difference can be detected between them. 



A still more remarkable case was observed in crosses be- 

 tween varieties of wheat of different grain-color. Red crossed 

 with white gave ordinarily all red in Fi and three red to one 

 white in F2, but a certain native Swedish sort gave only red 



