The process by which a nucleus divides, resulting in the segregation of the genome to opposite poles of a dividing cell.
Nuclear divisions occur in both mitosis and meiosis. In mitosis, the result is the division of duplicated copies of genome into two. In meiosis, nuclear division occurs twice, dividing the originally single nucleus into four nuclei that are genetically different from one another.
Compare: cell division
See also: mitosis, meiosis