An Introduction to a Biology 



was the oilspring of a hybrid and an albino. I took those 

 individuals to be hybrids which resembled the first crosses 

 {F^} in coat and eye colour — i.e. in the possession of a coloured 

 coat and pigmented eye. 



In mating hybrids of this generation (i^g) ^ ^^ ^^^ P^^' 

 viously look up their ancestry in books containing their 

 genealogical record, so that mice of the categories HH and 

 HA were mated at random ; in this way three kinds of crosses 

 were made : HH x HH, HH x HA, and HA X HA. In 

 each type of union a hybrid was mated with a hybrid, as I 

 believed at the time ; and as on Mendelian theory there is 

 no difference between the gametic constitution of DR pro- 

 duced by DR X DR and DR with parentage DR x RR, I 

 argued ^ that, if that theory were true, each type of union 

 would produce a fraternity, half of which would be composed 

 of hybrids, a quarter of which would be composed of pink- 

 eyed mice with coloured coats, while the remaining quarter 

 would consist of albinos ; on the other hand, it was evident 

 that on Galton's theory of heredity the proportion would 

 not only not be the same in each of the three cases, but 

 would differ in direct proportion to the amount of albino 

 blood in the parents of the population. The subjoined table 

 gives, together with the actual result, the proportions of 

 albinos as predicted by the two theories. In calculating the 

 Galtonian prediction I have not taken into account any 

 generations more remote than the great-great-grandparental.^ 



^ Biometrika, Vol. 3, pp. 23-5. 



2 I thank Mr. J. T. Wadsworth for checking this simple calculation. 



148 



