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Lakovaara, S. (Department of Genetics, University of Oulu, SF-90100 Oulu 10, Finland), Saura, A., Lankinen, P., Pohjola, Liisa and Lokki, J. The use of isoenzymes in tracing evolution and in classifying Drosophilidae. Zool. Scr. 5 (3–4): 173–179, 1976.—Studies on the genetic constitution of natural populations of organisms have shown that these populations are extensively polymorphic at gene loci coding for enzymes. Much of this polymorphism detected by electrophoresing enzyme proteins is, however, not useful in classifying organisms, even though in general species differ from each other more than populations within a species. Good diagnostic characters are monomorphic species-specific genes and their products. Finding these characters requires a thorough study of many populations of the species being studied. Once these characters have been found they can be used in assigning single individuals into different taxa. Electrophoresis of enzymes and allozyme differences between species can also be used in tracing the evolution of organisms. On the basis of allozymes a new phylogeny is proposed for the Drosophila obscura species group. Traditionally this group has been divided into two subgroups, obscura and affinis. Genetic characters divide this species group into three evolutionary lineages. The first lineage comprises the Eurasian obscura subgroup, the second the American affinis subgroup and the third the American obscura subgroup. D. alpina and D, helvetica, which belong to the obscura and affinis subgroups, respectively, are not appreciably related to any other species.