Elimination of Mongrel Blood. 



133 



May mongrel blood be absolutely eliminated? If so, what are 

 the chances that an F 3 offspring by the pure-sire method in man 

 will carry absolutely no mongrel blood? The calculations are 

 based upon the following assumptions: (1) that the haploid 

 number of chromosomes in man is 12 ; (2) that all of the hereditary 

 traits in the human species are carried by these 12 chromosomes, 

 which, barring crossing over, non-disjunction and other special 

 phenomena, segregate and recombine intact according to Mende- 

 lian expectation; (3) that the breeding between the pure sire 

 and the mixed dams of a given chromosome-number in a given filial 

 generation continues in proportion to the probable frequency of 

 the latter's occurrence in each particular generation; (4) that all 

 types of dams possess the same average fecundity. 



The chance that in man a given individual offspring produced by 

 the continuation of the pure-sire method will carry absolutely no 

 mongrel blood, i. e., will possess absolutely no chromosomes descended 

 from the mongrel dam is measured by the following series: 



Fi 0 to infinity Fa I : 0.463 



F2 1:4095.000 F7 1:0.208 



F3 1 : 30.568 Fs 1 : 0.100 



F4 1 : 3-964 F» 1 : 0.049 



F5 1 : 1. 169 F10 1 : 0.025 



The chance that in man a given individual offspring produced by 

 the continuation of the pure-sire method will carry not more than one 

 (i. e., none or one out of a possible twelve) mongrel chromosome is 

 measured by the following series: 



Fi 1 to infinity Fe 1 : 0.055 



Fs 1:314.077 F 7 1:0.014 



F 3 1 : 5-313 F 8 1 : 0.005 



F4 1 : 0.829 F» 1 : 0.002 



F6 1: 0.205 F10 1:0.001 



Summary. 



1. Mongrel " blood " is eliminated by the pure-sire method not 

 by "quartering out," but in segments, in degree governed by the 

 relative ontogenetic potency of the particular chromosomes elimi- 

 nated. 



2. The degree of elimination of mongrel " blood " by the pure- 

 sire method depends upon two factors, (a) the number of chromo- 



