Abstract: DSN1 is a SPB component that functions in yeast chromosome segregation process. It has been shown to be of haploinsufficient but its nature of gene dosage sensitivity was yet to be established. This study indicated that gene dosage variation of it has caused abnormalities in both cellular growth and nuclear division. Alteration of cell size and compromised budding index were part of the phenotypic manifestations. Changes in gene copy number also led to nuclear division and separation errors such as aneuploidy and nuclear disjunction. The results of this study provide direct evidence of the function of DSN1 in chromosomal segregation process. Gene dosage sensitivity of the gene also implied that its gene product would be forming complex with another protein.