Cytological Analysis of the Parasexual Cycle in Dictyostelium discoideum

Abstract

SUMMARY: We have developed a rapid and simple technique for examining chromosomes of the cellular slime mould Dictyostelium discoideum, based on standard cytological techniques involving fixation in methanol/acetic acid and staining with Giemsa stain. The haploid chromosome set is analysed. Four diploid strains are examined cytologically in order to determine their ploidal stability and to determine the pathway of haploidization in the parasexual cycle. In the absence of cloning, diploid strains eventually revert to haploid. Haploidization proceeds via transient aneuploidy. Aneuploids of all classes, n+1 through to 2n+2, have been demonstrated cytologically. It is concluded that aneuploids can divide but that they are unstable and readily lose chromosomes to form aneuploids of lower chromosome numbers and eventually haploids. Hence, the process of haploidization is similar to that found in the parasexual cycle of Aspergillus nidulans.