A system for the study of meiotic non-disjunction using Sordaria bervicolis

A system is described for the study of abnormal chromosome segregation in Sordaria brevicolis. The system utilizes two complementing alleles of the b₁ locus on linkage group II. Abnormal asci containing black disomic ascospores were detected which fall into two main categories. (a) Non disjunctional asci in which the disomic spores were present together with an equal number of abortive (nullosomic) spores and (b) asci in which an extra replication of the chromosomes had occurred resulting in pseudo-wild types being formed without accompanying spore abortion. Calculations indicate that the non-disjunction frequencies at the first and second divisions of meiosis are 4.25×10⁻⁴ and 4.35×10⁻⁴ respectively. It is suggested that the system is potentially a valuable one both for the study of meiotic non-disjunction and other causes of aneuploidy.