312 



GENERAL BIOLOGY 



DandR, germ cells of one hybrid parent 

 I X I * n cnance combination with 



DandR, germ cells of the other hybrid parent 

 give in the second (F 2 ) generation, 



DD + 2DR + RR in the proportion, (3 black: i white) n. 



Otherwise stated, if any two of these hybrids be bred 

 together there result the following possible combinations 

 of their characters in their offspring (the characters D and 

 R of one parent being underscored in order to distinguish 

 sources) : 



D and D, uniting, give D, a pure dominant] 

 DandR, " " DRl. , ., Iblack 



RandD, DR) hybnds J 



R and R, " R, a pure recessive white. 



Of the black individuals it is obvious that there are two 

 classes although all look alike; for one individual out of 

 every three is, like the white, pure bred containing sex cells 

 of one kind only, while the other two are still hybrid in 

 character. The further results of intercrossing of like with 

 like in successive generations is indicated by the following 

 table: 



Parents. Offspring, (mated like with like.) 



Generation I Gen. II Gen. Ill Gen. IV 



( iD. D D 



fiD.. .D 



R 



iR 



(iD 



| 2 n 



D(R) 



