CHAPTER II 

 TYPES OF MENDELIAN HEREDITY 



Experience has shown that Mendelian inheritance 

 apphes to all sorts of characters, structural, physio- 

 logical, pathological, and psychological ; to characters 

 peculiar to the egg, to the young, and even to old 

 age; to length of hfe; to fundamental taxonomic 

 characters as well as to ^'superficial" characters; and 

 to characters intimately concerned in maintaining 

 the hfe of the individual, as well as to characters which 

 apparently do not influence survival. Some of these 

 different types and their mode of inheritance will be 

 briefly described, but since the general principles in- 

 volved are more important than the kind of character 

 that is affected, the results will be treated under 

 general headings. 



Dominance and Recessiveness 



The four-o'clock (Mirabihs jalapa) has a white and 

 a red-flowered variety. If these are crossed the hy- 

 brid is pink in color. The pink hybrid inbred (self- 

 fertihzed in this case) gives in the next generation 

 (F2) one red, to two pink, to one white (Fig. 14). 

 Owing to the intermediate color of the hybrid (or 

 heterozygote) it is impossible to say that either 

 color dominates the other. The factor for red and 



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