Size inheritance and the pure line theory. 



By W. E. Castle, Belmont (Massachusetts, U.S.A.) 



(Eingegangen am 20. Februar 1914.) 



In 1909 my pupils and I published some detailed quantitative 

 observations upon the inheritance of certain size-characters in rabbits. 

 Our observations were made upon ear-size, total body-weight, and bone 

 dimensions. We found that when large-sized rabbits are crossed with 

 those of smaller size, offspring are produced of intermediate size. The 

 next, or Fa generation of offspring is also of intermediate size and, so 

 far as our observations went, not more variable than the Fi generation. 

 To this latter point, however, we gave no special attention partly because 

 we realized that our data were at that time insufficient and partly 

 because our primary object had been to determine the occurrence or 

 non-occurrence of Meudelian inheritance as regards size characters. Our 

 conclusion was that size inheritance is non-Meudelian, as Meudelism 

 was up to that time understood. We adopted an existing term for such 

 inheritance, namely that of blending inheritance, and straightway 

 instituted further experiments to discover if possible more about its 

 nature. It is true that as early as 1902 Bateson (p. 152) had clearly 

 pointed out that size differences may possibly be due to multiple Mendelian 

 allelomorphs as follows: 



"At first sight it seems that cases of continuous variations, lileiuling 

 in their hereditary transmission, form a class apart from those to which 

 Mendel's principles apply. But, though it may well be so, the questiou 

 cannot be so easily disposed of. The essence of the Mendelian con- 

 ception is, as we have seen, that each gamete may transmit one allelo- 

 morph pure. So long as each heterozygote can only exhibit one allelo- 

 morphic character, the dominant, we can from a study of the heterozygotes 

 and their offspring demonstrate the purity of the gametes. But dominance 

 is a distinct and subordinate phenomenon. We readily perceive that 

 the heterozygotes may show either of the parental characters dis- 



Induktive Abstammungs- und Vererbungslehre. XU. 16 



