Chapter 11 



GENETICAL CHARACTERS 



The following tabulation divides genetical characters into five 

 arbitrary categories: 



Terminal characters 



Quantitative characters 



Lethal genes 



1. Morphology and color (Higher 

 plants and animals) 



2. Colonial morphology (Micro- 

 organisms) 



1. Weight 



2. Size 



3. Number of parts 



The affected haploid segregant 

 or homozygote dies. 



Biochemical and physio- 

 logical 



1. Fermentative ability 



2. Vitamin deficiencies 



3. Amino acid deficiencies 



4. Nucleic acid component defi- 

 ciencies 



5. Antigenic composition 



6. Male sterility 



7. Self-sterility 



8. Mating types 



Modifiers 1. Suppressors 



Recessive genes which trans- 

 form recessive phenotypes 

 into wild type. 

 2. Plus and minus modifiers 



Enhance or diminish the ex- 

 pression of a given character 



TERMINAL CHARACTERS 

 Terminal characters affect structures produced late in develop- 

 ment without reducing the viability of the organism under ordinary 

 culture conditions; eye color in flies, flower color in plants, and 

 colonial morphology in bacteria and yeasts, are standard examples 

 of this type of mutant. There is considerable variation of colonial 



11-1 



