THE GENOMIC ORIGIN OF THE UNPAIRED CHROMOSOMES IN TRITICALE

Abstract

Differential staining of telomeric rye heterochromatin and telocentric chromosomes was used to identify chromosomes unpaired at the 1st meiotic metaphase [MI] of hexaploid triticale (.times. Triticosecale Wittmack). Both approaches showed that it was the rye chromosomes which were seen as univalents. Differences in the rate of pairing from triticale to triticale were mostly explained by variation in the pairing of the rye genome. Within the rye genome chromosome arms with telomeric heterochromatin showed pairing rates much lower than chromosome arms lacking heterochromatin. Wheat telocentrics and heterochromatin-free rye telocentrics which showed intermediate levels of pairing failure (65-90%) had mostly terminal chiasmata. Rye telocentrics with large heterochromatin bands on the telomeres had mostly nonterminal chiasmata and very low pairing (5-35%). The presence of heterochromatin on certain telomeres of rye chromosomes blocks the formation of terminal chiasmata resulting in desynapsis and univalents at MI.