Fate of multicentric and ring chromosomes induced by a new gametocidal factor located on chromosome 4M(g) of Aegilops geniculata

A new gametocidal (Gc) factor was identified on chromosome 4M(g) of Aegilop s geniculata Roth. When transferred to Chinese Spring wheat, monosomic and disomic Triticum aestivum-Ae. geniculata chromosome 4M(g) addition plants u ndergo regular first and second meiotic divisions. Male gametogenesis in di somic 4M(g) addition plants also is normal. However, chromosome breakage an d anaphase bridges were observed at ana/telophase of the first (29%) and se cond (11%) pollen mitosis in monosomic 4M(g) addition plants. Gc- induced m ulticentric and ring chromosomes can be transmitted to the offspring and in itiate breakage fusion bridge (BFB) cycles in dividing root tip meristem ce lls of the derived sporophytes. The fate of multicentric and ring chromosom es was analyzed in root meristems at different time intervals after seed ge rmination. The majority of the BFB cycles ceased about 32 days after germin ation. Broken chromosome ends were healed either by the fusion of a centric and an acentric fragment forming terminal translocation chromosomes or as deficiencies or telocentric chromosomes. Lack of cytologically detectable t elomeric repeats at the stabilized newly broken termini suggests that chrom osome healing by addition of telomeric repeats may be a gradual process.