caa a22 4500 445846003 CHVBK 20180317145359.0 cr unu---uuuuu 170323e20110201xx s 000 0 eng 10.1007/s10709-010-9533-1 doi (NATIONALLICENCE)springer-10.1007/s10709-010-9533-1 Structure and meiotic behaviour of B chromosomes in Sphaerium corneum/S. nucleus complex (Bivalvia: Sphaeriidae) [Elektronische Daten] [Tereza Kořínková, Jiří Král] Karyotypes of eight populations of Sphaerium corneum and two populations of S. nucleus (Bivalvia: Sphaeriidae) from central Europe were compared. The basic set of these hermaphroditic molluscs is formed by 30 biarmed autosomes and exhibits only slight interpopulational variation in morphology. These differences are not species-specific. One pair of nucleolar organiser regions was detected by silver staining. The prophase and metaphase of the first meiotic division is highly modified in both species. Pachytene is followed by a diffuse stage, characterized by decondensation of chromosomes and by enhanced metabolic activity. The diffuse stage has not been reported in bivalves so far. Bivalents of the following stages are achiasmatic both in the testicular and ovarian part of the gonad. The two species are further peculiar for occurrence of B chromosomes, which is a rare phenomenon in organisms with achiasmatic meiotic systems. The small metacentric B chromosomes exhibit intra- and interindividual variability in number, they show irregular meiotic pairing and segregation (formation of bivalents or univalents), and possess larger proportional amount of constitutive heterochromatin than the A chromosomes. Interestingly, the B chromosomes also undergo decondensation during the diffuse stage like A chromosomes which may indicate their transcriptional activity. Springer Science+Business Media B.V., 2010 Achiasmatic meiosis nationallicence B chromosome nationallicence Bivalve nationallicence Constitutive heterochromatin nationallicence Diffuse stage nationallicence Sphaerium nationallicence Kořínková Tereza Department of Zoology, Faculty of Science, Charles University, Viničná 7, 128 44, Praha 2, Czech Republic aut Král Jiří Department of Genetics and Microbiology, Faculty of Science, Charles University, Viničná 5, 128 44, Praha 2, Czech Republic aut Genetica Springer Netherlands 139/2(2011-02-01), 155-165 0016-6707 139:2<155 2011 139 10709 https://doi.org/10.1007/s10709-010-9533-1 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10709-010-9533-1 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Kořínková Tereza Department of Zoology, Faculty of Science, Charles University, Viničná 7, 128 44, Praha 2, Czech Republic aut NATIONALLICENCE 700 1- Král Jiří Department of Genetics and Microbiology, Faculty of Science, Charles University, Viničná 5, 128 44, Praha 2, Czech Republic aut NATIONALLICENCE 773 0- Genetica Springer Netherlands 139/2(2011-02-01), 155-165 0016-6707 139:2<155 2011 139 10709 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer