Chromosome structure and pairing preferences in autotetraploid rye (Secale cereale)

The influence of chromosome structure upon pairing behaviour during meiosis was investigated by comparing four autotetraploid genotypes of rye (Secale cereale) containing homologous chromosome sets with different degrees of structural similarity. The series provided a range of genotypes that, at one extreme, contained structurally identical chromosome sets and, at the other extreme, sets that are certainly more heterozygous in the genic sense and probably also more diverse from a purely structural viewpoint. Relative frequencies of pairing configurations at meiotic prophase and metaphase I were compared by electron microscopy of whole-mount surface-spread synaptonemal complex complements and light microscopy of squash preparations. Despite unexpectedly low quadrivalent frequencies over all four genotypes, higher mean bivalent frequencies appeared to be associated with greater homologue diversity. In other words, greater structural divergence between chromosome sets appears to facilitate more efficient discrimination between homologous and identical chromosomes that drives the formation of bivalents. Statistical comparisons were not able to confirm in some cases the significance of the observed pattern of pairing behaviour.