Meiosis in haploid rye: Extensive synapsis and low chiasma frequency

Abstract

Extensive synaptonemal complex formation was found at prophase I in whole mount spread preparations of a spontaneous haploid rye, Secale cereale, with values of up to 87.8 per cent of the chromosome complement synapsed. Pairing-partner switches were frequent, giving rise to multiple 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 heterochromatin were more frequent than between the remaining arms. The observation of recombinant chromosomes for telomeric C-bands at anaphase I indicates that metaphase I bonds are true chiasmata. The correspondence between the location of pairing initiation sites and chiasmata indicates that early synapsis could be confined to homologous regions. © The Genetical Society of Great Britain.