The presence of three full sets of chromosomes in the nuclear material of a cell. This occurs during the pollination of plants, in which one of the three male gametes which passes into the plant fuses with the two polar bodies in the ovum of the other plant, forming one triploid cell from three haploid ones. This later forms the food store which is part of the seed. This is called Double Fertilization, as the fusing of these gametes occurs parallel to the fusing of the male and female gametes to form the diploid zygote.

An animal with triploid DNA could form through a fault in either meiosis or during the development of the zygote, although this individual would most likely be aborted, die very soon after being born, be badly disabled or be unable to reproduce.