In flowering plants, fertilization occurs through pollination, i.e. the transfer of pollen from the anther to the stigma of a plant. The pollen contains the male gametes (sperm cells) that are transferred into the female gametophyte (i.e. ovules of flowering plants and the cones of coniferous plants) via the pollen tube. In regard to pollination, the ovum may be fertilized either by cross-pollination or by self-pollination.
Cross-pollination refers to the mode of fertilization wherein the sperm from the pollen (from the anther) of a plant is transferred to the stigma of the flower of another plant.
In cross-pollination, new genotypes are produced more than in self-pollination. It helps increase genetic diversity. It also prevents inbreeding depression, i.e. when the biological fitness in a given population is reduced as a result of inbreeding. Thus, it helps reduce the probability of a plant species producing offspring subject to disease or genetic disadvantages due to unfavorable recessive alleles. The more diverse the genes or alleles in the gene pool, the better they are protected against extinction.