engleski

Size variation and peculiar behaviour of nucleolar organizer region in Quercus species

Heteromorphy of the nucleolar organizing region (NOR) in the karyotypes of Q. petreae, Q. robur and Q. pubescens were noticed. This heteromorphy concerned size variation and rarely number variation of NORs in the karyotypes of different individuals of the same species. In general, Quercus species contain one pair of satellite chromosomes (SAT-chromosomes) bearing NORs on the terminal position. In the karyotypes of some individuals NORs were frequently detached from SAT-chromosomes and appeared as free spherical bright yellow fragments in the cells after chromomycin staining. Because of this behaviour we had suspected them as "B-chromosomes" in our previous report. In mitotic anaphase, such fragments formed bridges of extended sticky connecting threads with thier SAT-chromosomes of were lagging after anaphase group but it seemed that they were never elimated . On the other hand, fragments never occurred free in meiosis and two chromomycin positive dots were always located on the terminal site of the two chromosomes forming a bivalent. Recently applied fluorescent hybridisation in situ revealed hybridization signals of 18S RNA probe on the two SAT-chromosomes or fragments, respectively, proving its role as nucleolar organizers. Present investigation carry out NOR's size variation and frequency of detached NORs in comparison with NORs located on SAT-chromosomes in different individuals of the same species.

NOR; detached satellite; oaks; Quercus species; meiosis

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