Enzyme variation in T. brucei ssp. II. Evidence for T. b. rhodesiense being a set of variants of T. b. brucei.

A collection of stocks of Trypanosoma brucei rhodesiense isolated in Kenya have been examined for electrophoretic variation in 20 enzymes. The results obtained have been analysed in order to determine whether these trypanosomes are diploid and undergo mating and to determine the genetic distance between T. b. rhodesiense, T. b. brucei and T. b. gambiense. The enzyme electrophoretic markers were further used in experiments involving cyclically transmitted mixtures of stocks aimed at detecting genetic exchange in the laboratory. No genetic exchange was detected. Two novel features of the enzyme electrophoretic results were found. Firstly, the stocks of T. b. rhodesiense were considerably more homogeneous than equivalent collections of stocks of T. b. brucei and secondly, all the stocks examined were heterozygous for two alleles of alkaline phosphatase and showed an excess of heterozygotes at the phosphoglucomutase locus. The degree to which these features are typical of T. b. rhodesiense has been examined in relation to previously published data. The results obtained strongly support the view that T. b. rhodesiense is a set of variants of T. b. brucei rather than a subspecies and a working hypothesis as to the relationship between T. b. brucei and T. b. rhodesiense is proposed to explain the enzyme electrophoretic data obtained.