College of Liberal Arts & Social Sciences Theses and Dissertations

Graduation Date


Document Type


Department/Program Conferring Degree

Biological Sciences


Meiosis, Nondisjunction, Drosophila melanogaster, altered disjunction (ald)


Meiosis is a specialized form of cellular division in which the gametes are formed. During female meiosis I, homologous chromosomes must coorient to opposite poles to ensure proper segregation, otherwise nondisjunction can occur which would form aneuploid gametes. The recent discovery that chromosomes do in fact congress prior to metaphase I arrest in Drosophila requires a reexamination of the mechanisms behind nondisjunction. To do this, a series of altered disjunction (ald) mutant alleles generated by imprecise excision of a P element in the 5’ UTR were compared through a genetic nondisjunction assay and cytological examinations for the chromosomes' coorientation. These excision mutants have been shown to be competent to complete congression, but produce varying levels of wildtype Ald protein, which results in varying nondisjunction rates, ranging from wildtype to near-random segregation, all within an isogenic background. The hypothesis was that if nondisjunction is set up by congression errors that result in maloriented homologs at metaphase arrest, then the predicted outcome would be that the rates of genetic nondisjunction and malorientation should be equal. To test this hypothesis, the nondisjunction rates were measured genetically and the chromosomes' coorientation at metaphase I arrest was measured by scoring Immuno-FISH probed oocytes. The data showed high correlation between the genetic and cytological nondisjunction rates. The sequence analysis showed that various components of the P-element, P{GS:13084}, sequence were inserted into each line. Further research of meiosis I and mechanisms by which nondisjunction occurs could potentially provide a better understanding of many medical problems.