C-bands and chiasma distribution in Scilla siberica (Hyacinthaceae)

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Abstract
The distribution of chiasmata and their relationship to heterochromatic segments in Scilla siberica (Hyacinthaceae) have been analyzed in pollen mother cell meiosis by means of a Giemsa C-banding technique. All chromosomes could be identified in the meiotic cells. C-bands have a clear effect on chiasma distribution. Regions adjacent to intercalary homomorphic C-bands showed higher chiasma frequencies than other euchromatic regions. Chiasma distribution in bivalents of chromosome variants without these intercalary C-bands is different from those with C-bands. Strongly heterozygous C-blocks lead to a pronounced reduction of chiasma frequency in their vicinity. Mechanical clues for this are found in pachytene pairing behaviour of heterozygous C-bands, which also indicates that euchromatin is constant and C-bands are variable and additional segments. Within one anther, equational separations of C-band heteromorphisms were less than expected from corresponding metaphase I bonds, presumably because of a lower chiasma frequency in early meiotic cells. Heteromorphic intercalary C-bands show that chiasmata do not terminalize. Only at the onset of anaphase I does chiasma resolution result in transitory configurations reminiscent of terminalization.Key words: Scilla siberica, C-bands, meiotic recombination.

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