IN-BREEDING 241 



desirable not only to perpetuate this improved character 

 but to breed animals that have this quality in as pure 

 and dominant a state as in the original animal. This 

 can be accomplished by in-breeding. No other method 

 is available which will so quickly and certainly result in 

 producing offspring of similar or identical blood lines. 

 The history of animal-breeding is rich in instances of 

 great animals, famous for their individual excellence 

 but more famous because they have left a heritage 

 of potent " blood " which has established a new and 

 better strain or even a new breed. We need only 

 recall the names of Favourite, the Shorthorn bull, Justin 

 Morgan, the founder of the Morgan breed, Hambletonian 

 10, the forerunner of the American trotting horse, and 

 scores of individuals of lesser note belonging to practically 

 every modern breed. In many of the instances to which 

 reference is here made, the great individuals would never 

 have become famous if breeders had not recognized their 

 peculiar excellences and have insured the perpetuation 

 of their valuable characters by in-breeding. 



224. In-breeding and prepotency. The prepotency 

 of animals is increased by in-breeding. There is unanimity 

 among investigators and practical breeders on this point. 

 By continuous in-breeding we may " breed out " less 

 desirable qualities, that is, in the light of mendelism the 

 characters in the germ-plasm tend to become homozygous. 

 In-bred animals are " pure-bred " animals not only in the 

 parlance of the breeder but also from the standpoint of 

 genetics. Mating animals of diverse characters tends 

 to destroy prepotency. Mixing the blood of animals of 

 widely differing characteristics results in making the 

 constituent characters of the germ-plasm heterozygous. 

 The cross-bred animal is never prepotent. 



