IX 



Heredity in Protozoa' 



Inheritance within the strain 

 Strains, races, biotypes 

 Tendency toward genetic uniformity 

 Apparently spontaneous changes 

 Environmentally induced changes 



Genetic effects of syngamy 



Syngamy in haploid flagellates 

 Syngamy in diploid Protozoa 



Genetic effects of conjugation 

 General effects of conjugation 

 Cytoplasmic lag in biparental inherit- 

 ance 

 The micronuclcus in conjugation 

 Behavior of mating tvpes in conjugation 

 Behavior of antigenic types in conjuga- 

 tion 



Genetic significance of endomixis, autog- 

 amy, and cytogamy 

 P.ndomixis 

 Autogamy 

 Cytogamy 



Genetic significance of the macronucleus 



The cytoplasm in inheritance 



The killer trait in Paramecium aurelia 

 Mating types and cytoplasmic inherit- 

 ance 

 Antigenic types and cytoplasmic inherit- 

 ance 



Literature cited 



INHERITANCE WITHIN 

 THE STRAIN 



Strains, races, biotypes 



A 



PROTOZOAN SPECIES is composed of strains (races, biotypes, or 

 stocks) which differ among themselves in hereditary traits. Such races 

 have long been known in Paramecium (24, 25), Difflugia (2.1), Arcella (21) 

 and C entropy xis (70). Observations on mating types of ciliates (Chapter 

 II) have shown that a conventional species also may include varieties 

 which are completely, or almost completely, unable to interbreed. This 

 situation creates taxonomic problems which cannot be solved until more 

 is known about mating types and the comparative characteristics of these 

 different ciliate strains. Racial characteristics are of various kinds. Dif- 



^ Re\ lews of protozoan genetics have been published by Jennings (28, 29, 30) and 

 Sonneborn (76, 81). 



506 



