MEIOSIS IN HAPLOID RYE - EXTENSIVE SYNAPSIS AND LOW CHIASMA FREQUENCY

Extensive synaptonemal complex formation was found at prophase I in wh ole mount spread preparations of a spontaneous haploid rye, Secale cer eale, with values of up to 87.8 per cent of the chromosome complement synapsed. Fairing-partner switches were frequent, giving rise to multi ple associations in which all or most of the chromosomes were involved . However, the distribution of synaptonemal complex stretches suggests that synapsis does not occur at random. The frequency of multivalents and the mean frequency of bonded arms at metaphase I were 0.03 and 0. 39, respectively. Associations between chromosome arms without heteroc hromatin were more frequent than between the remaining arms. The obser vation of recombinant chromosomes for telomeric C-bands at anaphase I indicates that metaphase I bonds are true chiasmata. The correspondenc e between the location of pairing initiation sites and chiasmata indic ates that early synapsis could be confined to homologous regions.