A systematic analysis of parthenogenetic (PG) cell fate within the central nervous system (CNS) was made throughout fetal development and neonatal and adult life. Chimeras were made between PG embryos carrying a ubiquitously expressed lacZ transgene and normal fertilized embryos. After detailed histological analysis, we find that the developmental potential of PG cells is spatially restricted to certain parts of the brain. PG cells are prevalent in telencephalic structures and are largely excluded from diencephalic structures, especially the hypothalamus. These spatial restrictions are established early in development. Behavioral studies with chimeras identified an increase in male aggression when the proportion of PG cells in the brain was high. These studies demonstrate that imprinted genes play key roles in development of the CNS and may be involved in behavior.