ABSTRACT
Paramecium was the first protozoan to be studied genetically. Today, other single-celled eukaryotes, such as unicellular fungi and algae, trypanosomes, Plasmodium and other ciliates such as Tetrahymena and Euplotes, are also favourite objects of study. Studies on the genetics of Paramecium began in the late 1800s, but since conjugation could not be controlled, progress was slow. When Sonneborn discovered mating types in Paramecium (Sonneborn, 1937) and began the first controlled crosses between hereditarily diverse strains, these studies quickly led to a confirmation of Mendel's principles in the lower organisms, but also revealed a series of surprising and unique phenomena. Today, the techniques of molecular biology are revealing the structure of the macronucleus and giving us new insights into these unusual phenomena.
