EFFECTS OF INBREEDHsTG AND CROSSBREEDING. 



45 



heterozygosis will remain true indefinitely. Summing up, a random- 

 bred stock derived from n inbred families will have th less superiority 



over its inbred ancestry than the first cross or a random-bred stock 

 from which the inbred families might have been derived without 

 selection. 



COMPARISON OF RESULTS WITH THEORY. 



In the foregoing theoretical considerations we have assumed that 

 the characteristics depend on the heredity of the progeny produced 

 by the mating in question. It will be recalled, however, that we 

 found good reason for beheving that most of the characteristics in 

 the experiments with guinea pigs were really determined wholly or in 

 part by the parents, in most cases the dam, as far as these character- 

 istics were genetic at all. In a character determined wholly by the 

 dam. Experiments CO and CA belong with the inbreds, CC, AC, and 

 Cl represent the first cross, and C2 represents the first generation of 



Fig. 26. — The percentage of heterozygosis following matings among inbred families of the types PQ x RS 

 PQ X QR, and PQ x PQ. Original families, x of type AA and y of type aa. 



renewed inbreedmg. In characters determined partly by the parents 

 and partly by the progeny we can easily find the relations which are 

 to be expected by combining the expectations based on the breeding 

 of the dam and sire with those based on the progeny. Table 13 

 shows the expectation in certain cases, while Figure 27 presents some 

 of the same conclusions graphically. 



