MOLECULAR CYTOGENETIC CHARACTERISTICS OF CHIRONOMID B-CHROMOSOME
(DIPTERA, CHIRONOMIDAE)
M. T. Siirin, N. B. Rubtzov, T. V. Karamysheva, A. V. Katokhin, D. A. Karagodin, I. I. Kiknadze
Institute of Cytology and Genetics, Siberian Branch of RAS, Novosibirsk;
e-mail: rubt@bionet.nsc.ru
Morphological and molecular study of B-chromosomes of three Chironomus species (siblings Ch.
borokensis and Ch. phumosus from plumosus group, and Ch. heterodentatus from
obtusidens group) was carried out. Morphological similarity of B-chromosome banding pattern and
telomer-centromeric region banding pattern of chromosome IV in Ch. borokensis was shown. Polytene
B-chromosomes of Ch. borokensis and Ch. heterodentatus were microdissected, and their DNA was
amplified using degenerate oligonucleotide primer polymerase chain reaction. Comparative analysis of the
localization of homologous B-chromosome DNA sequences of A- and B-polytene chromosomes was made using in situ
fluorescence hybridization. It has been shown that B-chromosomes in the studied species are composed mainly of
repetitive DNA sequences homologous to sequences of centromeric and telomeric DNA of A-chromosomes, and also
these of the mobile element NLRCthl. The B-chromosome DNA, homologous to sequences of DNA mobile element, was
scattered on A-chromosomes (more than 100 sites). No ribosomal DNA repeats were identified in B-chromosome.
Heterologous FISH of B-chromosome DNA to polytene A-chromosomes of Ch. thummi, a species lacking
B-chromosomes, enabled us to reveal the presence of numerous sites homologous to DNA of B-chromosomes. These are
mainly mobile element sites. An origin of B-chromosomes and pecularities of their organization in chironomids are
discussed.
Key words: B-chromosomes, FISH, Chironomus species
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