MULTIPLE FACTORS IN MENDELIAN INHERITANCE^ 



E. C. MacDOWELL 



Sheffield Scientific School 



From Osborn Zoological Laboratory, Yale University 

 HISTORICAL 



Since cases of simple Mendelian phenomena have been very 

 frequently described, the interest of the student of genetics has 

 shifted from the attempt to prove, or disprove, Mendelism to- 

 wards the investigation of the extent of the application of Men- 

 del's fundamental principles. Perhaps this is why the appar- 

 ent exclusion of anything Mendehan from size inheritance by 

 Castle's work on the ear length of rabbits, aroused so much in- 

 terest. Castle ('09) found that the ear lengths of rabbit offspring 

 were in general intermediate in relation to the parents. This 

 seemed to indicate a simple blending inheritance in which the 

 size-controlling elements from either parent were permanently 

 joined in the offspring, never to segregate. Yet in the same rab- 

 bits Mendelian ratios were being given and segregation was taking 

 place in the color of the hair. The appearance of a paper by H. 

 Nilsson-Ehle ('09) brought a new possible interpretation of the 

 ear length crosses. In this paper evidence was presented to 

 show that there may be two or more Mendelian factors for the 

 same character, which factors develop the character whether they 

 appear alone or in any combination with the others. 



Nilsson-Ehle found in certain crosses of oats and wheat in 

 which the colors of the glumes and seeds were considered, that 

 simple Mendelian ratios (3:1) were generally given, but in cer- 



' This paper is based on an investigation carried on in the Laboratory of Ge- 

 netics of the Bussey Institution with assistance from the Carnegie Institution of 

 Washington. A full report of the investigation has been submitted to the Car- 

 negie Institution for publication. This statement of some of its main features is 

 published by permission. For the conclusions drawn from the facts recorded the 

 author is alone responsible. 



177 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 16, NO. 2 

 FEBRUARY, 1914 



