MEIOTIC BEHAVIOR OF HOLOCENTRIC CHROMOSOMES - ORIENTATION AND SEGREGATION OF AUTOSOMES IN TRIATOMA-INFESTANS (HETEROPTERA)

The meiotic behaviour of the holocentric chromosomes of the heteropter an species Triatoma infestans has been analysed by means of orcein sta ining and C-banding on squashed spermatocytes. We have focused our ana lysis on chromosome 3, which shows a large distal heterochromatic band at one of the ends of both homologues. At metaphase I, and independen tly of the chiasma position, two alternative orientations have been ob served: either the heterochromatic or the euchromatic ends of both hom ologues are directed to opposite poles. At anaphase I, the kinetic act ivity is restricted to the same chromosome end (euchromatic or heteroc hromatic) of each homologue. The frequencies of these two alternatives are not random and differ significantly among the five individuals an alysed. However, the euchromatic ends present kinetic activity at a hi gher frequency than the heterochromatic ends. At metaphase II, half-bi valents also show the kinetic activity restricted to either of the chr omosome ends (euchromatic or heterochromatic). The frequencies of each alternative are inverted in anaphase II compared with those scored in anaphase I. Accordingly, those ends that present kinetic activity at anaphase I segregate reductionally during the first meiotic division a nd equationally during the second meiotic division. These results prov ide sound evidence on the meiotic behaviour of holocentric chromosomes , as regards the absence of chiasma terminalization and the modes of o rientation and segregation.