Meiotic recombination in the ZW pair of a tinamid bird shows a differential pattern compared with neognaths

The tinamid bird Nothura maculosa, along with other species of the order Tinamiformes and all of the existent ratites, form the infraclass Paleognathae, the most primitive living birds. Previous work has shown that in all studied Neognathae, the ZW pair shows strictly localized recombination in a very short pseudoautosomal region, while in paleognath birds, the ZW pairs have mostly free recombination. The present observations show that the ZW pair of N. maculosa has a recombination pattern departing from both neognaths and other Paleognath birds, as there is a single crossover but occurring at random points along a significant part of the long arm of the W chromosome. This recombination pattern agrees with the presence of intercalary and terminal heterochromatin in the W chromosome, suggesting an exceptional, additional step of recombination suppression.Key words: recombination, ZW pair, avian sex chromosomes, sex chromosome heteromorphism.

Rye heterochromatin. II. Characterization of a derivative from chromosome 1DS.1RL with a reduced amount of the major repeating sequence

Homoeologous recombination between wheat chromosomes and the long arm of chromosome 1R of rye present in a wheat background as the wheat–rye translocation, 1DS.1RL, has been reported. During the course of this study an unexpected plant (308-17), with a recombinant phenotype, arose from a control population where homoeologous pairing was thought to be suppressed. The putative recombinant chromosome in plant 308-17 carried two seed protein loci located on 1RL (namely, the rye Glu-R1 locus and a recently discovered globulin-like marker) but appeared to lack C-banded heterochromatin. Further investigation of this apparent recombinant chromosome in progeny of 308-17 using a cloned probe for the 350 family of rye heterochromatic sequence indicated that some terminal heterochromatin was still present but in a much reduced amount. Because it appears that only the terminal region has been changed, the modified chromosome in 308-17 most likely did not arise from homoeologous recombination but rather from some form of heterochromatin loss event, possibly involving an unequal sister chromatid exchange within the terminal heterochromatin of 1RL. Sister lines to plant 308-17 carrying Glu-R1 contained a normal amount of 1RL heterochromatin.Key words: rye–wheat, heterochromatin, recombinant, unequal sister chromatid exhange.