Chromosome studies. V. Diploidy and persistent chromosome relations in partheno‐produced Tettigidae (Apotettix eurycephalus and Paratettix texanus)

Abstract

Abstract Number of chromosomes is 13 (♂) and 14 (♀), the same as in biparentally produced relatives. In diploid groups from partheno‐produced individuals homologous chromosomes tend to lie together, as ‘doubles’ or separated but near each other. In biparentally produced individuals they have as marked a tendency to lie in oppósite halves of the plate. Chromosomes of an individual tend to persist in the same position from cell to cell in the partheno‐produced, with homologues side by side arranged about one center; in the biparentally produced, with seven single members arranged about each of two centers. In the partheno‐produced the cells of younger animals, or of the earlier stages of organs in older animals, have a larger proportion of ‘double’ chromosomes or closely associated homologues. These conditions suggest that the partheno‐produced individual arises from an egg with a single pronucleus in which there were seven ‘double’ or diad‐like chromosomes, and the biparentally produced from an egg with two pronuclei, each with seven ‘single’ chromosomes. The paired position of homologues in Diptera may be due to synapsis‐like tendencies in early cleavage, either as ‘hang‐over’ effects from the preceding meioses or a different type of synapsis mechanism in Diptera. Partheno‐produced male tettigids may be accounted for through non‐disjunction among the four parts of the sex tetrad.