18 HEREDITY. 



over, to look for facts, which the first man could have very 

 easily demonstrated himself. 



II 



itttttttuina 



I IS 



Ill 



II I i. Ill 



Fig. 2. 



A few matings of hooded rats which show the existence of a gene, 

 which is present in dark-hooded and absent from light-hooded animals. 

 Light-hooded children from dark-hooded parents (e.g. 44 and 50, from 47 

 and 3) give no dark-hooded offspring. Dark-hooded may be homozygous 

 or heterozygous for the gene. 



Young rats which are parents in any of the later matings shown, have 

 been given a distinguishing mark to facilitate finding their pedigree. 



There happened to be in our hooded-rats animals with, and 

 others without one gene. The presence or absence of which, 

 exerted a marked influence on the extent of the pigmented 



