An investigation into the origins of meiotic aneuploidy using ascus analysis

Abstract

SUMMARY: Aneuploidy can result from a variety of defects at meiosis. Results are presented of crosses of Sordaria brevicollis in which aneuploid spores are detected through complementation of spore colour mutants at the buff or grey-6 loci on linkage groups II and IV respectively. By using ascus analysis, the underlying cause of the aneuploidy can be deduced in many cases. Thus non-conjuction (pairing failure) and non-disjunction at the first meiotic division, premature centromere division, non-disjunction at the second division, and pre-meiotic errors such as extra replication of the chromosomes can be distinguished. Both linkage groups were found to give a similar proportion of the different errors. Non-conjunction and first-division non-disjunction formed 60–70% of detectable cases, whilst premature centromere division and second-division non-disjunction comprised 10% and 5% of aneuploids respectively. However, only a small proportion of second-division errors are detected.It is proposed that the systems described in this paper can form the basis of a valuable screening method for detecting agents which increase aneuploid frequency. The advantages and disadvantages of using lower eukaryotes in this way are discussed.