34 



INHERITANCE; OF COAT-PIGMENTS AND COAT-PATTERNS 



the hooded and Irish patterns, Doncaster (:o6), after an extended experience, 

 says (p. 216): "Only once have I had any hesitation in classing a rat as 

 belonging to one or the other." Yet we have seen that by cross-breeding 

 and selection these same discontinuous groups can be made continuous by 

 the production of any desired number of intermediate groups, each varying 

 continuously about a different mode. 



Again, though the inheritance is clearly Mendelian, when hooded and Irish 

 rats are crossed, the gametes formed by cross-breds are not pure, but modified, 

 each extracted pattern being changed somewhat in the direction of that 

 pattern with which it was associated in the cross-bred parent. This means 

 simply that the inheritance, though in the main alternative, is to some extent 

 blending. 



Since it is impossible to make a sharp distinction between continuous and 

 discontinuous variations, as well as between blending and alternative inherit- 

 ance, it is fallacious to assign all evolutionary progress to one sort of variation 

 or to one sort of inheritance. 



TABLES. 



TABLE i. Actually different classes into which we may expect the five visibly different 



classes o\ albino and partial-albino rats to fall. 

 [Twenty-two of the twenty-seven classes enumerated have been proved to exist.] 



B, black; G, gray; H, hooded; I, Irish; W, total albinism. Symbols indicating unseen 

 recessive characters are placed within parentheses ( ), those indicating characters latent 

 in albinos are placed within brackets [ ]. 



When two symbols only are used the first refers to color, the second to coat-pattern. 



When more than two symbols stand together within brackets, those which refer to 

 color are placed at the left of a hyphen, those referring to pattern at its right. 



Total albinism is indicated by W. When albinism is recessive with other characters 

 in pigmented individuals, the W will be separated by a period from the symbols designating 

 the other characters. 



The numerals prefixed to the several class-designations indicate the expected frequencies 

 of the classes when individuals are mated inter se which have the characters indicated by 

 the designation GI (W.BH). 



