title: Cytogenetics of the bleak (Alburnus alburnus), with special emphasis on the B chromosomes.
abstract: Some of the largest B chromosomes so far discovered in vertebrates are present in the cyprinid fish Alburnus alburnus. Previous cytogenetic analyses revealed a diploid chromosome number of 2n = 50. In addition, in some individuals one or two unusually large B chromosomes are present. Two morphologically different types of B chromosomes were observed. The frequency of animals bearing a supernumerary chromosome was found to vary considerably between different populations. A more detailed analysis of the A and B chromosomes of A. alburnus by conventional banding techniques, as well as fluorescence in-situ hybridization (FISH) with the telomeric DNA repeats (GGGTTA)7/(TAACCC)7, 18S + 28S rDNA and 5S rDNA were performed in the present study. Furthermore, a B chromosome-specific DNA probe obtained by amplified length polymorphism (AFLP) was hybridized on metaphases of A. alburnus carrying supernumerary B chromosomes. The banding analyses showed that the B chromosomes are completely heterochromatic, consist of GC-rich DNA sequences, replicate their DNA in the very late S-phase of the cell cycle and are composed mainly of a specific retrotransposable DNA element. Finally, blood probes from A. alburnus were collected for DNA-flow cytometric measurements. It could be shown that the huge supernumerary chromosomes represent nearly 10% of the total genome size of A. alburnus.
authors.affiliation: Department of Human Genetics, University of Würzburg, Biozentrum, Am Hubland, D-97074, Würzburg, Germany. m.schmid@biozentrum.uni-wuerzburg.de
authors.forename: M
authors.initials: M
authors.lastname: Schmid
authors.forename: C G
authors.initials: CG
authors.lastname: Ziegler
authors.forename: C
authors.initials: C
authors.lastname: Steinlein
authors.forename: I
authors.initials: I
authors.lastname: Nanda
authors.forename: M
authors.initials: M
authors.lastname: Schartl
mesh_terms: D000818:Animals; D002871:Chromosome Banding; D002875:Chromosomes; D003530:Cyprinidae / Q000235:genetics*; D020732:Cytogenetic Analysis; D015342:DNA Probes; D004275:DNA, Ribosomal / Q000032:analysis; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D008297:Male; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D012339:RNA, Ribosomal, 28S / Q000235:genetics; D012341:RNA, Ribosomal, 5S / Q000235:genetics; D012091:Repetitive Sequences, Nucleic Acid; D016615:Telomere
chemical_list: D015342:DNA Probes; D004275:DNA, Ribosomal; D012337:RNA, Ribosomal, 18S; D012339:RNA, Ribosomal, 28S; D012341:RNA, Ribosomal, 5S