Adjustment of Lateral Element Lengths in Hybrids of Lolium Temulentum x L. Multiflorum

Meiotic chromosomes: integrating structure and function

Meiotic chromosomes have been studied for many years, in part because of the fundamental life processes they represent, but also because meiosis involves the formation of homolog pairs, a feature which greatly facilitates the study of chromosome behavior. The complex events involved in homolog juxtaposition necessitate prolongation of prophase, thus permitting resolution of events that are temporally compressed in the mitotic cycle. Furthermore, once homologs are paired, the chromosomes are connected by a specific structure: the synaptonemal complex. Finally, interaction of homologs includes recombination at the DNA level, which is intimately linked to structural features of the chromosomes. In consequence, recombination-related events report on diverse aspects of chromosome morphogenesis, notably relationships between sisters, development of axial structure, and variations in chromatin status. The current article reviews recent information on these topics in an historical context. This juxtaposition has suggested new relationships between structure and function. Additional issues were addressed in a previous chapter (551).

The pattern of homoeologous recombination in triploid hybrids of Lolium multiflorum with Festuca pratensis

Homoeologous chromosomes of Lolium-Festuca hybrids are capable of frequent meiotic pairing and recombination. The frequency and distribution of recombination was studied by genomic in situ hybridization in backcross progenies of reciprocal triploid hybrids of Lolium multiflorum with Festuca pratensis. Significant differences in the male transmission of the parental and translocated chromosomes were observed depending on the cytoplasm of the F1 hybrids and the ploidy level of the female test cross partner. The frequency of intergeneric translocations in the progeny indicated that, on average, there must have been at least 4.5 homoeologous arms paired in the F1 hybrids; the actual frequency might have been higher because of pre- or post-zygotic selection against the F. pratensis chromatin, which probably eliminated certain gametes with Festuca-Lolium translocations. Both parental species are known for localized distal chiasmata, but the intergeneric translocation breakpoints were distributed along the entire lengths of the chromosome arms. The change in the distribution of homoeologous recombination might have been related to different pairing initiation of homologues and homoeologues. It probably resulted from allocation of additional chiasmata to chromosome arms and produced a net increase in recombination.Key words: homoeologous exchanges, Lolium-Festuca, translocations, recombination.