In contrast to most other vertebrates,teleost fish exhibit an unparalleled capacity to generate stem cells in both the intact and the injured adult brain.My research is focused on the occurrence, the extent and the fate of aneuploid cells (genome-modified individual cells characterized by the loss or gain of whole chromosomes) generated in the teleostean brain. Aneuploidy arises through various chromosome segregation defects during the mitotic divisions of newly-generated cells in the adult brain. Aneuploidy is observed in ~80% of the newly-generated stem cells of the adult brain,but occurs at a very low rate in liver tissue, as shown by metaphase chromosome spreads and flow-cytometric DNA content analysis. The mitotic machinery of adult brain cells was examined for chromosome segregation defects which showed lagging chromosomes at metaphase and anaphase, as well as micronuclei and anaphase bridges,in the intact adult brain. In conclusion,my research demonstrates the evidence of the generation and maintenance of aneuploid cells in the adult fish brain that arise through chromosome missegregation which is a widespread phenomenon in the teleostean central nervous system.