Chemical Homologies Between Protozoa

SYNOPSIS. Nucleic acid hybridisation involving DNA samples was used to study relationships between various protozoa. The most hybridisation or nucleic acid homology was always in the homologous reaction between 2 DNA samples from the same source. It was concluded that all the protozoa tested have nucleotide sequences or genes in common with Paramecium aurelia. The ciliates could be placed in a sequence of decreasing homology relative to Paramecium: Tetrahymena, Colpidium, Stentor, Didinium, Dileptus, Blepharisma. Actinosphaerium had fewer sequences than any of the ciliates and the flagellate Euglena had the fewest sequences in common. The bacterium Aerobacter had none. Similar relationships were inferred from competitive hybridisation experiments; these relationships were also in general mirrored by morphologic relationships and overall G + C base compositions which ranged from 46% for Euglena to 32% for P. aurelia. These experiments, it is hoped, will contribute to studies on origins of the metazoa.