FACTS OP INHERITANCE 151 



' agouti ' ones, which bred inter se will produce 

 agouti, black, white (or else yellow) young, with 

 perhaps those of other new classes in addition. 

 Such a result as this puzzled Darwin, and would 

 naturally puzzle any one ; but in the light of 

 Mendel's law becomes capable of ready explanation. 

 The production of black pigment is a process in 

 which more than one unit character is concerned, 

 the production of a grey coat involves more 

 units still. . . . What was unknown to Mendel 

 has been made clear since 1900: that in many 

 cases two or more independent unit characters 

 must be present to produce a single visible 

 effect/' 



THE CASE OF ANDALUSIAN FOWLS. The pheno- 

 mena of Mendelian inheritance are well illustrated 

 in the case of the Blue Andalusian fowl. We quote 

 Mr. Punnett's account l : " The Andalusian has long 

 been known to possess an inconvenient peculiarity : 

 it will not breed true. It always throws ' wasters ' 

 of two sorts : blacks, and whites marked with some 

 black splashes. There are, therefore, three kinds 

 of Andalusians, and consequently six possible 

 types of mating among these three varieties. With 

 regard to the results of these types of mating, 

 careful experiment has brought out the following 

 facts : 



Blue x Blue gives Blacks, Blues, and Whites, in the ratiol : 2 : 1 . 

 Blue x Black , Blacks and Blues in equal numbers. 



Blue x White , 

 Black x Black . 

 White X White , 

 Black x White , 



Blues and Whites in equal numbers. 

 Blacks only. 

 Whites only. 

 Blues only. 



1 " Mendelism in Relation to Disease," Proc, Roy. Soc. 

 Medicine" (March 1908). 



