•  A variety of chromosome types, as defined by relative size and shape, were found to be present in the nucleus of each cell. Furthermore, there usually were two copies of each type of chromosome. This cell is called a diploid cell. •  All of the cells of an organism, excluding sperm cells, egg cells, and red blood cells, and all organisms of the same species, were observed to have the same number of chromosomes. • The number of chromosomes in any cell appeared to double immediately prior to the cell division processes of mitosis and cytokinesis, in which a single cell splits to form two identical offspring cells.