378 LINKAGE PHENOMENA 



Red-eyed hybrid females X red-eyed males. If the hy- 

 brid red-eyed females of the last paragraph are bred to 

 their red-eyed brothers (or any other red-eyed males) all 

 the daughters are red -eyed because they receive a domi- 

 nant " red " X from the father and either a " red " or a 

 " white " X from the hybrid mother. Half the sons are 

 red-eyed because they receive a " red " X from their 

 mother along with the inactive Y from the father. The 

 other half of the sons are white-eyed because they receive 

 a " white " X from their mother and an inactive Y from 

 the father. The accompanying figure (HI) should make 

 this point clear. 



Red-eyed Male X White-eyed Female. — Reference 

 to Fig. 112 shows that the hybrid daughters here receive 

 a " white " X from the mother and a " red " from the 

 father, and are therefore red-eyed. Sons receive a Y 

 from father and a " white " X from mother and are there- 

 fore white-eyed. If these white-eyed males are bred to 

 their hybrid red-eyed sisters half the daughters are red- 

 eyed hybrids and half are pure white-eyes. Likewise, 

 half the sons receive a " red " X from their hybrid mother 

 and a Y from their father and are red-eyed, and half re- 

 ceive a " white " X from the mother and a Y from the 

 father and are white-eyed. 



Summary of Principles of Heredity. 



1. The first law or principle states that the genes for 

 parental character-pairs segregate in the hybrid. 



2. The second principle goes a step further and states 

 that each pair of characters may segregate independently 

 of other pairs. 



3. The third principle is that independent segregation 

 is limited to pairs whose genes are in separate chromo- 

 some-pairs. 



4. The fourth principle is that characters whose genes 

 are in the same pair of chromosomes will be linked, i.e., 

 tend more or less strongly to remain together in heredity. 



