SEX IN UNICELLULAR ALGAE 127 



been pointed out by Patau (1941) and liartc (194S). In C. //loeivusii 

 the genetic behavior of eight ultraviolet-induced mutant characters 

 and of mating type has been investigated (Lewin, 1953); and evi- 

 dence for linkage was obtained between t and /, two mutant charac- 

 ters respectively affecting cell division and flagellar activity, and 

 between "p-aminobenzoic-less" and the mating-type locus. J. Harts- 

 horne (personal communication) has studied the genetics of an ultra- 

 violet-induced mutant "eyeless," and of tw^o suppressed semi-lethals 

 found in wild stocks of C. reinbardi. In this species, as in C. //loeiviisii 

 and in virtually all other organisms which have been studied, crossing- 

 over takes place between chromatids, and two or four different 

 haploid genotypes can be obtained from a single zygote. 



CONCLUSION 



Some of the greatest strides in the field of microbiology have 

 been made when a number of workers, using different approaches 

 and techniques, have concentrated on a single organism, such as 

 Neurospora or Escherichia coli. It might not be rash to predict that 

 similar progress will result from a concerted attack on the control of 

 sexuality in a suitable selected unicellular alga. Many problems 

 should be solved in this way, and others will inevitably arise; for the 

 simplicity of microorganisms is more apparent than real. 



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