INBREEDING EXPERIMENTS 



109 



througliout the course of the experiment (Fig. 27). The 

 whole series of inbreds compares well in this respect with 

 stock albinos for which the average litter size is 6.7. 

 Further there was a notable increase in longevity in line 

 A and a marked increase in line B. 



Average Size of Utter 



GENERATIONS 



^.^^ 



T^n t n I I I I I I I I J I r 111 III 



10 II 12 13 14 IS IS .17 IB le 20 11 22 23 2* 2S 



Fia. 27. — Graph showing the average size of litters produced in successive generations of 

 inbreeding albino rats by brother and sister matings. (After King.) 



The interpretation of these experiments is wholly in 

 accordance with Mendelian theory. Starting with stock 

 rats which from previous close breeding had already been 

 reduced to a high degree of homozygosity, inbreeding had 

 the tendency to accentuate this purity of type and to 

 segregate slight differences. By selection vigorous uni- 

 form strains were built up, strains somewhat larger, more 



