558 



GENERAL CONSIDERATIONS 



2. When the two hereditary units are unlike, the one which shows 

 its presence by a visible character may be called dominant and the other 

 recessive but in many cases there is incomplete dominance. 



3. In breeding individuals heterozygous for any pair of characters, 

 three kinds of offspring will be produced — those which are homozygous 

 and possess the dominant character; those which are homozygous and 

 possess the recessive character; and those which are heterozygous and 

 show the dominant character or intermediate stages of the dominant and 

 recessive characters (law of segregation). 



Homozygous Male Homozygous Female 



Primary f^ (^ Primary 



Spermatocyte 



Oocyte 



Sperm Cells - any one Egg Cell Polar Bodies 



Fertilized E^^l^ 



Produces 



Heterozygous Male or Heterozygous Females 

 Primary /^ 

 Spermatocyte 



Sperm ^ells 



Possible Comb/nat/ons 



Fig. 384. — Diagram showing the inheritance of unlike characters by a hybrid between two 

 homozygous but unlike parents and the results of interbreeding these hybrids. 



599. Hybrids. — In Chap. XXII reference was made to cross-fertihza- 

 tion and hybridization. A hybrid in the sense in which the term was there 

 used referred to the production of an offspring by two individuals belong- 

 ing to difTerent species. It is evident from what has just been stated that 

 we may also use the term hybrid in reference to heterozygous individuals 

 belonging to the same species. An animal may be a hybrid for certain 

 characteristics and yet be pure-blooded so far as the species or variety is 

 concerned, the characteristics which it possesses being recognized as 

 varying within the species. 



600. Distribution of Characteristics in Hybrids. — In crossing two 

 individuals homozygous for the same pair of characters it is evident that 



