Generation by a polymorphic supernumerary segment of recombination in a normally achiasmate proximal region in Acrotylus insubricus (Scopoli) (Orthoptera, Acrididae)

Abstract

Four of 20 males collected from a Spanish natural population of Acrotylus insubricus (Scopoli) present a supernumerary segment that is distally located in one of the chromosomes of the M9 bivalent. In meiosis this segment is positively heteropyenotic during the first prophase and reverses its pycnosis at first metaphase. The extra material shows "grey" staining after C-banding and fluoresces brightly with acridine orange. The nucleolar expression in this species is not affected by the presence of the supernumerary segment. However, it provokes a considerable alteration in the pattern of chiasma distribution in the M9 bivalent if compared with standard individuals. Certain aspects related to the possible structural influence of the segment in the displacement of the chiasmata are discussed.Key words: Acrotylus, supernumerary segment, chiasma distribution.