Fig. 1.

Comparative genomic hybridization (CGH) in mitotic and meiotic chromosomes of four water frog Pelophylax esculentus males. M1 (a), M2 (b-d), M3 (e-g, j) and M4 (h, i). CGH clearly distinguished chromosomes of the parental species, P. ridibundus (red) and P. lessonae (green). a Mitotic prometaphase. b Haploid mitotic metaphase after elimination of the ridibundus genome. c Diplotene. d Meiotic metaphase I. e, f, g, h Late meiotic prophase I. i, j Meiotic metaphase I showing bivalent-like configurations and univalents. Solid arrowheads indicate the smallest submetacentric chromosome pair with marked ridibundus-specific repetitive DNA in the lessonae-derived chromosome set, arrows indicate bivalent-like configurations between two different parental genomes, open arrowheads indicate bivalent-like configurations within one parental genome, asterisks indicate univalents. Scale bars equal 10 μm