120 Hagedourn. 



before I had produced any other yellow females. I mated the great- 

 grandmother to one of the yellows and she produced 1 1 agouti young. 

 As however the record is incomplete, it might be that the loss of 

 factor B had taken place before I caught the wild ancestors of the 

 strain, and that in every generation there had been one or more Bb 

 heterozygous mice. 



By mating one of these yellows (AbBCDEFGH) (No i8) to chocolate 

 (ABcDEFgH), I obtained agoutis (AABbCcDDEEFFGgHH), which on mating 

 inter se gave mice with all possible combinations of these three factors, 

 ABCDEFGH, agouti; AbCDEFGH, yellow agouti hke the Original (No i8); 



ABcDEFGH, cinnamon (No l); ABCDEFgH, black (No 15); AbcDEFGH, 



clear orange (No 24); AbCDEFgH, tortoise; and ABcDEFgH, chocolate 

 (No 16), and orange, AbcDEFgH in ratio of about : 27 : 9 : 9 : 9 : 3 : 3 : 3 : i. 



Mutual repulsion between two factors. 



Ordinaril}/, as can be seen from the tables, individuals, hetero- 

 zygous for two factors, produce four kinds of gametes, such having 

 both factors, such having one only, such having the other only, and 

 such without either the one or the other. Such heterozygotes, when 

 mated to individuals, lacking both factors, produce the corresponding 

 four kinds of offspring. As can be seen from the tables, mice hetero- 

 zygous for both A and G, AaBBCCDDEEFFGgHH, when mated to albinos 

 without G, that is aaBBCCDDEEFFggHH, produce four sorts of offspring, 

 in equal proportions. Agoutis (AaGg), Blacks (Aagg), Albinos with G 

 (aaGg) and albinos without G, (aagg). 



But in one special series of experiments, some of the first experi- 

 ments of the kind I did with mice, the facts were quite different. I 

 bred a strain of agouti mice, heterozygous both in A and in G, which 

 strain had originated by a mutation, as I have just told. These 

 agoutis did not produce agouti, black and albinos of two kinds in 

 the proportion 9:3:4, but in the proportion 2:1:1. Adding the 

 number of young produced from such mice 1 got 73 agouti, 37 blacks, 

 32 albinos. In the course of the experiments thirteen of these albinos 

 have been tested by mating them to black. Without exception they 

 have given black, or equal numbers of black and albino young, 

 depending upon the purity of the black used. But never has one 

 of these albinos produced a single agouti young in a mating with 

 black. Counting together the coloured young of such families I get 

 89 black young. 



