94 



GENETICS AND EUGENICS 



classes, including three individuals, will show one dominant 

 and one recessive character, viz., colored and long; two 

 more classes, including three individuals, will show the other 

 dominant and the other recessive character, viz., short and 

 albino; and lastly, one class, including a single individual, 

 will show the two recessive characters, long and albino. The 



Fig. 39. Diagram to explain the simultaneous and independent inheritance of colored fur (O and 



short hair («S) in the cross shown in Figs. 35-38. 



four apparent classes, or, as Johannsen calls them, phenq- 

 types, will accordingly be as 9:3:3:1. 



One individual in each of these four classes will, if mated 

 with an individual like itself, breed true, for it is homozygous, 

 containing only like units. The double recessive class, long 

 albino, of course contains only homozygous individuals, but 

 in each class which shows a dominant unit, heterozygous 

 individuals outnumber homozygous ones, as 2 : 1, or 8 : 1. 



Now the breeder who by means of crosses has produced a 

 new type of animal wishes, of course, to " fix " it, — that is, 



