Fig. 3

Localization of rDNA clusters in spread chromosome preparations of three Leptidea species by FISH with 18S rDNA probe. Chromosomes were counterstained with DAPI (blue). Arrows show hybridization signals of the 18S rDNA probe (red); asterisks indicate DAPI-positive blocks of heterochromatin. a Mitotic metaphase of L. juvernica male (2n = 90); the inset in the upper right corner shows the pachytene NOR-bivalent with a large interstitial rDNA cluster. b Mitotic metaphase of L. reali female (2n = 52); the inset in the upper right corner shows the pachytene NOR-bivalent with a large terminal rDNA cluster. c Male mitotic metaphase (2n = 69) with a typical hybridization pattern found in the offspring of one L. sinapis female. Figures (d–g) show a variable pattern in the offspring of another L. sinapis female: (d) mitotic metaphase of male offspring (2n = 71); (e) hybridization signals on pachytene chromosomes of the same male offspring (schematic drawing shows the structure of a trivalent carrying two out of three rDNA clusters); (f) mitotic metaphase of female offspring (2n = 73); (g) hybridization signals on pachytene chromosomes of the same female offspring (schematic drawing shows the structure of a bivalent heterozygous for a terminal rDNA cluster). Scale bar = 10 μm