i8 



HEREDITY AND EUGENICS 



half their germ cells. If two such persons mate 

 together, it will be seen from the following diagram 

 (Fig, 6) that half the germ cells of each will be normal 

 and half carr}- the defect. 



This will give four combinations of germ cells 

 occurring with equal frequency. Three of them, or 



FeeblemindecA 

 parent 



Germ cells 

 all F 



Cro 



Normal 

 parent. 



all N 



ss 



N(F) 



Fig. 5. — Result of Cross between a Dominant and a 

 Recessive Character in F^. 



on the average three-fourths of the offspring, will 

 be normal, the other fourth will be feeble-minded. 

 Moreover, of the normals tw^o-thirds will be carrying 

 feeble-mindedness as a recessive character while the 

 other third will be untainted. Further, it is clear 



Unions oF germ cells. 

 25 X N N 



25 % N F 



25 % N F 



^ (F) ^^ ^^^"'^_— — ^^ 25 % r F 



50 % F 

 Fig. 6. — Results of above Cross in F., 



that if the Mendelian behaviour is strictly adhered 

 to two feeble-minded parents can have only feeble- 

 minded offspring. The exceptions to this rule, if 

 they exist, are so few as to be negligible. For a further 

 account of feeble-mindedness see p. 149. 



There is no doubt that the germ plasm of any human 



