18 



HEREDITY. 



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

 easily demonstrated himself. 



tJili.ittiitili.lo.a 



r 49 *I25 



fit 



269 270 268 267 



m H 



An -A A/j An 



44 ^"50 I \bt ^170 



An 4 4 4 4 4 ( ; i 4 4' 



f'A; I A< 4 4 4 4 4 4 A) Ac Ao Ao A; A; Aa 

 .. Ill 1 "111 WJJJJ1 



no 



• >,9 



*4«l "^260 ^2 5? ^263 ^265 " r 25« ^262^261 r 268 *" 264 





258 



26! 



lit 



3 ^26P^304^D» ^HOI ^303^00 ^302 



™00~30 



Av Ai w As °Ai A; Af A? Ac 



fJJIJJJMS, 



I3J 



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 



