title: Meiotic and mitotic instability of two EMS-produced centric fragments in the haplodiploid wasp Nasonia vitripennis.
abstract: Terminal deletions that result in chromosomal fragments with centromeres (centric fragments) are relatively easy to generate and study in the haplodiploid insect Nasonia. We investigated the transmission stability of two chromosomal fragments generated by chemical mutagenesis. Visible mutations at the R locus (peach-233 and St-DR) and a linked body-colour mutant (purple) were used to track transmission of the centric fragments (which lack the purple locus and are wild-type at the R locus). Transmission rates in meiotic oogenesis were low (medians 0.15-0.18) and comparable to previous data on centric fragments in this species. The homologous chromosome genetic background strongly affected meiotic stability of one centric fragment (CF2) but not the other (CF1). Specifically, in peach/scarlet R locus heterozygous females, CF2 showed a normal segregation proportion with the chromosome bearing the scarlet allele (0.16), but near complete failure to segregate with peach (0.0002). Data show that this is due to loss of CF2 in eggs receiving peach, rather than to preferential segregation of CF2 with scarlet or mortality of CF2-bearing males. CF1 shows typical segregation ratios with both chromosomes. We hypothesize that deletions (or rearrangements) associated with the peach-233 mutant inhibit proper pairing and segregation of CF2. Consistent with the model, CF2 did segregate with chromosomes that had undergone recombination between peach and purple (a body-colour mutation 10 cM from peach), indicating that the domains inhibiting segregation are closely linked to peach. Mitotic instability also differed between the two fragments; reduced mitotic stability may relate to absence of telomeres on these centric fragments. Given the relative ease of generating and tracking terminal deletions in Nasonia, we propose this as a good system for studying mitotic and meiotic stability of centric fragments. Finally, results are discussed in relation to the evolution of B chromosomes from centric fragments.
authors.affiliation: Equipe Ecologie Evolutive, UMR-CNRS 5561 Biogéosciences, Université de Bourgogne, 6 boulevard Gabriel, 21000 Dijon, France. mjperrot@u-bourgogne.fr
authors.forename: M J
authors.initials: MJ
authors.lastname: Perrot-Minnot
authors.forename: J H
authors.initials: JH
authors.lastname: Werren
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002875:Chromosomes; D003433:Crosses, Genetic; D005260:Female; D006824:Hybridization, Genetic; D008297:Male; D008540:Meiosis / Q000235:genetics; D008938:Mitosis / Q000235:genetics; D009030:Mosaicism; D010641:Phenotype; D011003:Ploidies; D013045:Species Specificity; D014863:Wasps / Q000235:genetics*