Summary: Electrophoretically demonstrable variation in 12 enzymes was studied in more than 1600 isolates of from human and animal sources and in 123 strains of the four species of All 12 enzymes were polymorphic; and the number of allozymes (mobility variants), which were equated with alleles, averaged 9.3 per locus in For species, the mean number of alleles was 2.9 per locus. Some 77% of the allozymes recorded in were shared with A total of 302 unique genotypic combinations of alleles over the 12 loci (electrophoretic types, ETs) was distinguished, of which 279 represented and 23 were Among electrophoretic types, mean allelic diversity per locus was 0.52 for and 0.29 for It was estimated that there are, on the average, about 0.3 detectable codon differences per locus between pairs of strains of and which is roughly equivalent to 1.2 amino acid differences per enzyme. Evidence that the enzyme loci studied are a random sample of the genome is provided by a significant positive correlation between estimates of genetic divergence between pairs of strains obtained by DNA reassociation tests and estimates of genetic distance between the same strains based on electrophoresis.

A principal components analysis of allozyme profiles revealed that the 302 ETs fall into three overlapping clusters, reflecting strong non-random associations of alleles, largely at four loci. Each of the four ETs of that have been most frequently recovered from natural populations has an allozyme profile that is very similar to, or identical with, the hypothetical modal ET of one of the groups. ETs of fall into two of the groups. No biological significance can at present be attributed to the genetic structure revealed by multilocus electrophoretic techniques. The electrophoretic data are fully compatible with other molecular and more conventional evidence of a close affinity between and and they raise questions regarding the present assignments of certain strains to species. In support of evidence from DNA reassociation tests and serotyping, the present study suggests that is homogeneous in chromosomal genotype.


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