Segregation of the Univalent X Chromosome in the Two-Striped Planthopper Acanalonia bivittata

Abstract

Chromosomes pair with their homologues to form a bivalent in meiosis I. The formation of bivalent chromosomes, alignment on the metaphase plate, and segregation during anaphase I is critical for correct cell division and production of haploid gametes, yet exceptions to the rule of bivalent formation exist. Here, we studied the segregation of the univalent X chromosome in the two-striped plant hopper Acanalonia bivittata (Hemiptera, Auchenorrhyncha). The species identification was verified through DNA barcoding, and the chromosome number is consistent with previously published karyotypes for the species. We show that A. bivittata male primary spermatocytes have a univalent X chromosome that displays independent and delayed segregation. Univalent segregation was observed to occur after that of the autosomes during early anaphase I and was associated with the loss of microtubule connections to one spindle pole. This work contributes to our knowledge of how chromosomes that lack a pairing partner can be segregated in an environment where they are surrounded by correctly segregating bivalents.