ISSN 2079-0597, Russian Journal of Genetics: Applied Research, 2016, Vol. 6, No. 2, pp. 163–168. © Pleiades Publishing, Ltd., 2016. Original Russian Text © S.V. Mylnikov, S.V. Zhirov, 2015, published in Ecologicheskaya Genetika, 2015, Vol. 13, No. 1, pp. 3–9. 163 In memory of P.Ya. Shvartsman INTRODUCTION The advance in cytological methods has allowed for an insight into the shape and number of chromosomes in many animal and plant species. A new area of sci- ence, karyosystematics, has emerged and has allowed an update and clarifications on the phylogenetic sys- tem constructed based on the morphological criteria (White, 1973). In most cases, the number of chromo- somes is an adequate specific feature for a species. Characteristic of each species is a definite karyotype, i.e., the number and shape of the metaphase chromo- somes. For some organisms, interphase nuclei are also suitable for analysis of this kind due to polyteny, i.e., multiple chromosome doubling without cell division. In this process, the genes in the chromosomes line up and the concentrations of the expressed gene products in these cells increase several thousandfold. The chro- mosomes themselves acquire a characteristic dark and light banding detectable by certain dyes with an affin- ity for heterochromatin. The banding pattern deter- mined by the alternation of the dark (heterochroma- tin) and light (euchromatin) bands and interbands, respectively, is unique for each species (Kiknadze, 1971). The research into the karyotype structure of individ- ual dipteran species that carry the polytene chromo- some in several organs allows certain problems associ- ated with the mechanisms involved in the genome’s evolutionary rearrangement to be solved. The major cause underlying the karyotypic divergence is chromo- some mutations, among which Robertsonian rear- rangements—reciprocal exchanges of chromosome regions (Robertson, 1916)—are an important compo- nent. A special case of such rearrangements is the recip- rocal exchanges of whole chromosome arms and tan- dem fusions of telomeres, which alters the combina- tions of chromosome arms as well as the number of chromosomes and, correspondingly, the number of chromosome arms. The cytocomplexes, groups of closely related species that originated due to such exchanges (Keyl, 1962), have been discovered in the Chironomidae family. The species that form different cytocomplexes differ in either the diploid number of chromosomes or pairwise combinations of the chromo- some arms. On the other hand, irregular chromosome associations via terminal regions are formed in some species in the salivary gland’s somatic cells, thereby hin- dering the identification of the species-specific diploid chromosome number. Such complications are typical in the situations when it is difficult to get reliable infor- mation when studying the germline cells. For example, the mitotic and meiotic chromosomes from the chi- ronomid gonads and supraesophageal ganglia are very small, and the routine squash preparations fail to give satisfactory results providing an unambiguous interpre- tation (Petrova and Chubareva, 1978). A Statistical Approach to the Problem of the Taxonomic Status and Evolutionary Potential of a Non-Biting Midge, Prodiamesa olivacea Meigen, 1818 (Diptera, Chironomidae, Prodiamesinae) Based on Karyotype Analysis S. V. Mylnikov a and S. V. Zhirov b a St. Petersburg State University, St. Petersburg, 199034 Russia b Zoological Institute, Russian Academy of Sciences, St. Petersburg, 199034 Russia e-mail: s.mylnikov@spbu.ru, svzhiroff@mail.ru Received December 15, 2014; in final form, March 16, 2015 Abstract—The frequency of the contacts between polytene chromosomes via their centromeric and telom- eric regions in the karyotype of the non-biting midge Prodiamesa olivacea has been analyzed. The fact that the groups of centromeric contacts are nonrandom and match the diploid chromosome number, equal to ten, has been statistically confirmed. The species is announced as a transitional form that evolves towards a reduc- tion in the chromosome number. Keywords: Prodiamesa olivacea, polytene chromosomes, diploid number of chromosomes, irregular chromo- some associations, chromocenter, χ 2 test DOI: 10.1134/S2079059716020076