Fig. 3

Meiosis in hybrid-33 (pachytene to metaphase II) after FISH mapping with 5S (red) and 18S–26S (green) rDNA sequences and sequential GISH using total genomic T. ambiguum DNA (green). Chromosomes are counter stained with DAPI (grey scale or blue). a-b. A pachytene cell after DAPI staining (a, grey scale) and FISH (b). Thickness differences among chromatin threads represent variability in the number of synapsed chromosomes or chromatids. In a, arrows indicate irregular synapsis; b. shows an unpaired T. occidentale NOR chromosome (arrow) and three synapsed T. ambiguum NOR chromosomes (arrowhead). c-e. A metaphase I cell; c. DAPI-stained (grey scale), d-e. FISH and sequential GISH, respectively. Synaptic anomalies are apparent as multivalents and scattered univalents. f. Three examples of anomalous pairing selected from other metaphase I cells. A homoeologous bivalent between T. occidentale and T. ambiguum NOR chromosomes after DAPI staining and FISH (top), a nonhomologous intergenomic trivalent after GISH (centre), and a homologous trivalent of 5S rDNA carrying T. ambiguum chromosomes (bottom). g-h. Anaphase I Type 1 cell after DAPI staining (g grey scale) and FISH (h) showing complete poleward segregation of chromosomes apart from several sister chromatid laggards. Guidelines in g denote PSSC in T. occidentale and T. ambiguum univalents identifiable in h. i. AI-Type1 cell after FISH showing a T. occidentale NOR chromosome with a translocated additional 5S rDNA signal (enlarged in the inset, DAPI stained, left, FISH, right). j-k. AI-Type2 cell after DAPI staining (j) and FISH (k) showing partial poleward chromosome segregation. l-m. AI-Type3 cell after DAPI staining (l) and FISH (m) with intact chromosomes and separated sister chromatids, showing complete failure of anaphase I segregation. The arrow in l shows sister chromatid separation of a T. occidentale derived NOR univalent (identifiable in m). n-o. MII-Type1 cell after DAPI staining (n) and FISH (o) showing daughter nuclei with chromosomes surrounded by precociously separated sister chromatids. p-q. MII-Type2 cell after DAPI staining (p) and FISH (q) showing partial anaphase I movement. r-s. MII-Type3 cell after DAPI staining (r) and FISH (s) showing no anaphase I movement. Intact chromosomes and precociously separated sister chromatids are visible. Scale bar: 10 μm