The onion species AUium amplectans includes both a triploid and a tetraploid variety. By light microscopy both varieties appear to have normal synapsis during pachytene of meiosis. However, the triploid does not form chiasmata and exhibits almost total asynapsis following pachytene. The tetraploid forms at least one chiasma per homologue and retains pairing through metaphase I. Electron-microsc...

ECENT studies of the highly differentiated pachytene chromosomes of R the tomato have indicated that this plant can be used in the analysis of chromosome structure in relation to chromosome behavior and gene location (BROWN 1949; BARTON 1950). In general, the twelve paired chromosomes of the tomato pachytene complement are differentiated into densely staining (chromatic) regions proximally on e...