NORMAL INHERITANCE 37 



containing the pigment determiner and half containing the 

 albino determiner. Now if two cross-bred grays, each carry- 

 ing an albino determiner, be mated, the two kinds of germ 

 cells (C and c) will come together purely at random and the 

 offspring will appear in the proportions of 1 pure-bred pig- 

 mented: 2 cross-bred pigmented: 1 pure-bred albino. The 

 visible classes will be 3 pigmented (containing C) : 1 albino. 



Gametes of father 

 C c 



Gametes 

 of mother 



CC 



Cc 



Cc 



Combinations among 

 the offspring 



An actual experiment of this sort (combined data from Little 

 {110) and Keeler {87)), produced 2994 pigmented young and 

 1029 albinos or a ratio of 2.91 to 1, the theoretical expecta- 

 tion being 3017.75 pigmented: 1005.75 albinos. 



Some of the mouse genes have more than two alternative 

 forms or different chemical states. The color gene {€) has 

 at least four such allelomorphs in mice. These are (1) normal 

 pigmentation (C), (2) chinchilla {c ch ), (3) extreme dilution 

 or Himalayan albinism {c H ), (4) complete albinism (c). 



Each member of the series dominates in crosses over those 

 which follow it in the same series. That is, when an animal 

 bears heredity for any two of these characters, the one 

 appearing first in the list will be expressed in the coat. For 

 example, if a chinchilla be crossed with an albino, the first 

 generation will be chinchillas and the second generation will 

 contain an average of 3 chinchillas to 1 albino. No more 

 than two members of such a factor series may exist in a 

 single individual (one in each of the two chomosomes making 

 up a particular pair). 



If a normally pigmented animal carrying a chinchilla 

 factor be crossed with an extreme-dilute animal carrying 

 albinism, the first generation will consist of equal numbers of 

 normally pigmented animals and of chinchillas. Half each of 



