Heredity in Protozoa 511 



the genetic significance of these induced changes remains uncertain. 

 Jollos considered them the result of cytoplasmic modification rather than 

 gene mutation — an interpretation with interesting implications. In re- 

 production by fission, an original mass of modified cytoplasm would 

 already be diluted several million times at the twentieth generation, and 

 some of these induced modifications have persisted for several hundred 

 generations after removal of the stimulus. It is inconceivable that modi- 

 fied cytoplasm could exert significant effects in such high dilutions. If 

 "Dauermodifikationen" are strictly cytoplasmic, the modified cytoplasm 

 obviously must reproduce itself in a sort of cytoplasmic inheritance. 



GENETIC EFFECTS OF 

 SYNGAMY 



Syngamy in haploid flagellates 



Meiosis appears to be zygotic in Phytomonadida, with the result 

 that heterozygous vegetative stages are eliminated by persistence of the 

 haploid chromosome number throughout most of the life-cycle. Since the 

 genotypic composition of the flagellate is indicated by its phenotype after 

 division of the zygote, the phytomonads may be favorable material for 

 the study of biochemical genetics because so many species can be grown 

 bacteria-free in media of known composition. The induction of mutations 

 in autotrophic and heterotrophic types might produce physiological 

 changes which could be analyzed genetically. Experimentally induced loss 

 of chlorophyll might make possible crosses between green and colorless 

 strains of the same species. Such matings might supply significant data on 

 the genetics and biochemistry of chlorophyll formation and perhaps on 

 cytoplasmic inheritance. Although such aspects of phytomonad genetics 

 have not been explored, the inheritance of morphological traits has been 

 traced in a few species. 



The first observations were reported by Pascher (55, 56) in two strains 

 of Chlamydomonas. In some cases, the lines derived from hybrid zygotes 

 were essentially identical with one parental type or the other. Occasion- 

 ally, some of the lines showed combinations of parental characteristics 

 and apparently represented new genetic combinations. 



Essentially the same pattern of inheritance was reported by Moewus 

 (50) in intraspecific and interspecific crosses of Polytoma pascheri and 

 P. uvella. Linkage of such features as size of the body and length of 

 flagella was described, and occasional crossing-over was reported. Similar 

 results were obtained with Chlomydomonas eugametos, C. paradoxa, C. 

 paupera, and C. pseudoparadoxa (51). Although these observations are 

 very interesting, they need confirmation because the validity of the data 

 on crossing-over has been questioned (58). 



