﻿6 DARBISHIRE, Mendelian and Biometric Theories. 



by the two theories : in calculating the Galtonian pre- 

 diction I have not taken into account any generations 

 more remote than the great-great-grandparental.f 



Type of 

 Parentage. 



Number of 

 Young. 



Mendelian 

 Expectation. 



Galtonian 

 Expectation. 



Actual 

 Result. 



HHxHH 



93 



25% 



9-37 % 



1075 % 



HHxHA 



107 



25% 



I7-96 % 



18-69 % 



HAxHA 



121 



25% 



26-56 % 



2479 % 



Before continuing my argument, I should like to dwell 

 for a little on the circumstances which led me to believe 

 that I was dealing in F 2 with hybrids and indeed with 

 heterozygotes in the strict Mendelian sense of the term. 

 In the first place these putative hybrids bore the same 

 features of coat and eye colour as the F x hybrids 

 exhibited ; secondly, they formed 50% of the F 2 generation,, 

 and lastly at least two upholders of Mendelian theory* 

 had asserted that the heterozygote was represented in 

 my experiment by the coloured mice with pigmented eyes. 

 To resume the thread : these results were brought 

 before the notice of a student of heredity whose first 

 question was, if there had ever resulted from the union of 

 two hybrids a family in which there were no albinos ; a 

 query to which an affirmative answer was given. Then 

 the following argument was used by my critic : ' The 

 only proof that a given individual is a hybrid is one 

 which is based on an examination of its gametic con- 

 stitution ; in the case of your mice you have no right to 

 say that a grey mouse with black eyes is a hybrid until 



* Castle and Allen., Proc. Amcr. Acad. Arts and Set. , Vol. 38 ; No. 21. 



1 1 thank Mr. J. T. Wadsworth for checking this simple calculation. 



