Colony formation assay of holoclones, parent PC3 and paraclones. Four holoclones and four paraclones were assayed in comparison to parental PC3 cells. Cells from each PC3 cell clone were seeded at low density in individual wells of a standard 6-well plate and grown for 6 days in normal serum medium. Colonies were visualized by crystal violet staining. For parental PC3 cells, a small number of highly stained and tightly packed colonies were observed, corresponding to 11% (8/81) of all colonies counted, representing holoclones within the overall PC3 cell population. Holoclones again produced more holoclones than parental PC3 cells, while holoclones were not formed from paraclones.