title: The evolution of a neo-XY1Y2 sex chromosome system by autosome-sex chromosome fusion in Dundocoris nodulicarinus Jacobs (Heteroptera: Aradidae: Carventinae).
abstract: Sibling subspecies of Dundocoris nodulicarinus, inhabiting different isolated indigenous evergreen forests in South Africa, have chromosome numbers of 2n(male) = 14XY, 9XY1Y2 and 7XY1Y2. The ancestral chromosome number of Dundocoris is probably 2n(male) = 28XY and several chromosome fusions were involved in the karyotype evolution of these taxa. The XY1Y2 sex chromosome system of the 9XY1Y2 D. nodulicarinus novenus originated by the fusion of a large autosome with the X-chromosome, forming a neo-X with the homologue of the fused autosome forming the neo-Y (=Y1) and the original Y-chromosome, the Y2. While the original X- and Y-chromosomes are heterochromatic and heteropycnotic during prophase I, the autosomal part of the neo-X and the neo-Y stay euchromatic and behave like a normal autosomal pair, forming synapsis and chiasmata. The XY1Y2 sex chromosome system of the 7XY1Y2 D. nodulicarinus septeni probably originated from the 9XY1Y2 karyotype when the homologous chromosomes of a small autosomal pair fused with the original X- and Y-chromosomes, respectively. In both the subspecies with the neo-XY1Y2 systems, the original sex chromosomes still undergo chromatid segregation at anaphase I (= post-reductional). The evolution and behaviour of the karyotypes and sex chromosome systems during the course of meiosis in the subspecies of D. nodulicarinus are described, discussed and illustrated.
authors.affiliation: Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa. dhjacobs@zoology.up.ac.za
authors.forename: D H
authors.initials: DH
authors.lastname: Jacobs
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D005260:Female; D005828:Genetics, Population; D006570:Heterochromatin; D020062:Heteroptera / Q000235:genetics*; D007621:Karyotyping; D008297:Male; D008540:Meiosis; D012726:Sexual Behavior, Animal; D014960:X Chromosome / Q000235:genetics*; D014998:Y Chromosome / Q000235:genetics*
chemical_list: D006570:Heterochromatin