[9] Sonneborn combined the skilled observation of a natural historian, with a deep interest in cellular, genetic, and organismic methodology.

[3] After completing his thesis in 1930 on the microscopic worm Stenostomum, Sonneborn began to study ciliated protozoa, particularly Paramecium aurelia.

[3][2] Mitochondria and chloroplasts along with other internal cellular organelles (Kappa particles) which had their own DNA were inherited but limited by their distribution in the cytoplasm at the time of cell division.

He showed that nuclear genes were necessary to perpetuate the killer trait, which depended on the presence of the cytoplasmic "kappa" factor.

Sonneborn also developed serotypes, each of which was associated with an independent genetic loci and a specific active gene.

[2] Sonneborn developed plasmagene theory, the idea that genes produce a self-reproducing entity that is retained through somatic cell divisions and lost in sexual reproduction.

These hair-like projections move together like dancers in a ballet and enable the single-celled organism to "swim" through the liquid in which it lives.

One of his popular lectures involved students enacting the process of protein synthesis during which the genetic code is translated into the sequential addition of amino acids to form a polypeptide.

[citation needed] His enthusiasm was infectious, and his lectures inspired students to study protozoa and algae.