132 



Scientific Proceedings (ioo). 



74 (1449) 



The relation between the number of chromosomes of a species 

 and the rate of elimination of mongrel blood 

 by the pure-sire method. 



By H. H. Laughlin (by invitation). 



[From the Eugenics Record Office, Cold Spring Harbor, N. Y.] 



When to the neglect of individual Mendelian characters, the 

 whole organism is taken into consideration, the common method of 

 indicating the degree of parental qualities is to refer to the pro- 

 portion of ' ' blood ' ' of one type or other which the particular offspring 

 possesses. Thus the Fi hybrid is called a "half-breed " or a "half- 

 blood." Such an hybrid, bred back to the pure ancestor, gives a 3/4 

 blood pure, or a 1/4 blood mongrel, offspring, and so on according 

 to the following schedule: 



Fi 1/2 blood. Fi 1/32 blood. 



Fi 1/4 " F« 1/64 



Fj 1/8 " Ft 1/128 " 



F4 1/16 " 



This nomenclature is used for all bisexual organisms. It is 

 interesting to note that according to this scheme, theoretically 

 there would always be a fraction of mongrel blood in each indi- 

 vidual of a herd or group produced by the pure-sire method, 

 regardless of the number of generations to which the process 

 might have been carried. As a matter of practice, however, it is 

 known that after a few generations the progeny of the pure-sire 

 method are admitted on equal terms into the variety or species 

 of the pure sire, and with no apparent injury to the purity of the 

 paternal race. Thus Shorthorn breeders formerly permitted the 

 registration of animals 31/32 pure. 



According to Deniker, the male progeny of the F 3 generation 

 of the mating of Spaniards of pure descent with Indians and part- 

 bloods resulted in an individual who for all racial considerations 

 was called a Spaniard and was taken into the social life of the 

 Spanish people. In mating with the negro races the same con- 

 summation is achieved in the F 4 generation. 1 



1 J. Deniker, "Races of Man," p. 542. 



